As'alamualaikum, this is just a little advice from me!
So firstly, erm you had that interest to go to a club, but you didn't go...why!?
Haven't you thought about it deeply... because you have that fear of Allah (swt).
You ended up going to the club...you fell into shaytaans trap.
This is just a Hadith for you to ponder upon..
Abdullah ibn Amr reported: The Prophet (pbuh) said,
“The pleasure of Allah is in the pleasure of the parents, and the displeasure of Allah is in the displeasure of the parents"
Source: Sunan At-Tirmidhi 1899
And Subhanallah! you wear the hijab. Hijab is a form of modesty and purity. The hijab is a shield, it is righteousness and shows that you have faith. It is also an act of obedience to Allah (swt) and His prophet (pbuh).
"going to go out or take my scarf off, i was like you know what - since im getting **** for it already I might as well do it." This is how shaytaan will get to you, he will make you think 'oh your getting sin for that anyway, so just take it off!"
He will work on you slowly, he'll make you commit minor sins..then eventually you'll start committing major sins. (listen to this video until 37:40)
https://youtu.be/FemDGxSwVcM?t=2046 At this point my advice would be perform sincere taubah, ask for forgiveness from Allah (swt). Sit on the prayer mat and reflect on what you have done..if you feel like crying, cry, and only cry to Him because Allah will surely listen to your duas and guide you.
Also control your nafs (desires) that is the biggest thing. if you can control your nafs then shaytaan wont be a problem.
So for example you went to the club, now that isn't your fault it happens we're not angels, we are humans we all make mistakes but Allah (swt) has given us a chance we have to make taubah. Do taubah and and promise yourself you wont do that again.
Hadith:
One of the companions of the prophet (pbuh) asked him:
How many steps away is Jannah?
The prophet (pbuh) replied:
Two steps away, put one of your foot on your nafs and your other foot will lead you to Jannah.
"I took the scarf off because 1) i dont believe in it, 2) if i WAS wearing the scarf i would a) present islam in a negative light and b) not enjoy my self and feel paranoid and feel out of place and everyone would stare at me"1) It dosnt matter if you believe in it or not, just think that your doing all this for the sake of Allah (swt). Make that intention, Allah will surely be happy with you.
2a) And why do you think your presenting Islam in a negative way?
2b) Other peoples opinions are not important, pleasing Allah (swt) is important. When this world ends no one will help you, when you depart from this world no one will be with you in the grave, it'll only be you and your deeds, so live in this world within the Shariah laws.
"I guess i feel bad because i let down my parents. i enjoyed the night though.
but coming back, letting it all sink in, it didn't feel real. in fact, if it wasn't for my aching joints i would've thought it was all a dream."
You are very lucky that Allah (swt) made you feel that guilt, that is also one of the greatest things that Allah (swt) can do to a believers heart. Imagine some people don't even get this feeling!
"but i still feel horrible. i've just been crying and crying. i only left the room to go toilet. i still haven't eaten since last night really." Cry to Allah (swt) and just repent with a true heart. Please do not harm yourself like that, don't starve because you feel down..
This body of yours is an amanah of Allah (swt). He has given this body to us to keep the soul safe, our bodies are just a empty case for the soul...the prophet (pbuh) has taught us to keep our bodies nourished as it is an amanah of Allah (swt), so keep you diet just right
"i felt like it was a one time thing,
i'd put it back on. but how can i? wouldn't that make me a
hypocrite? of course, there's also the point that
if i DO fully take it off, my parents WILL find out"Sister, like i have said before, shaytaan will slowly work on you...don't let him win! And no, how can you call yourself a hypocrite? This is all part of shaytaans plan, don't fall for his trap..you need to win over him!
Insh'Allah you don't fully take it off, i will make duaa for you..i advice you to make sincere taubah..and try wearing the hijab again, start off with a couple of days, then try wearing the hijab for a week. Don't think about what other people think, have the intention that you are doing it for Allah (swt) only.
"I'm just scared, and i feel stupid and i hate myself right now. i just want to end it all but that would do no good to anyone . i don't know what to do or how to feel." When getting ready for bed pray your night duas (+ Surah Al Mulk - youll be saved from the punishments of the grave). Wake up for Fajr and make dua in salaah, also when waking up in the morning, pray your morning duas (+ Surah Al Yasin - Allah will make your day easy, and hardships will go away)
Insh'Allah this helps x