I'm starting to doubt I did well in my exam ...is this only me??

I have recently done some gcses and when I came out of some exams I thought I did quite well, I knew they didn't go as well as my other exams but I thought I did alright and I was hoping I'd get a decent 8/9. But after I realised I lost about 4 marks on one question I started worrying about how I think I have done badly 😐 I know there is no point overthinking it but I can't get it off my mind....do you think I should listen to the initial positive thoughts I had straight after the exam and ignore the doubt that's crept in? (Bearing in mind I probs I lost 10ish marks overall and you have to lose 18 marks to get a borderline 9)

So firstly it's completely normal to feel this way. Its far better to have some nerves and wonder about things as opposed to being emotionally ambivalent. It shows that you care, and have an interest in the outcome. It's down to functionality; if the thoughts are so strong and frequent that they prevent you from doing day to day activities, then there is an issue and you should get help and support. This entire process is a learning experience and that includes the waiting for results. You learn who you are as a person when it comes to stress, coping mechanisms, all of it. There's an element of the serenity prayer at play here, principally, accept the things you can not change. No amount of worrying or thought will change the outcome. Believe in yourself and believe that whatever the result, you can turn it in to a positive outcome, because you know you can overcome any adversity.

Thank youuu for that 😊 what I'm really asking is should I try to believe that I did do quite well because that was the initial thought when I came straight out of the exam rather than fall into the self doubt that has crept in after (in other words have you ever thought you did good at first but then started doubting everything even like whether you numbered your questions correctly for it to all turn out okay in the end)

You are quite welcome. To more succinctly answer your question; I would not try to believe you did well, nor that you did badly. It is folly to try to find succour in the unkown. Believe what you know to be true, because there is solace in that. You know to be true that it is done, you applied yourself and committed yourself. What is, is and the only thing deserving of your peace of mind and belief, is that you will face what comes with courage and conviction.

I don't mean this in a rude way at all but is English not your first language or are you just a very well worded person, because what you have written is very well sculpted but I'm struggling to understand some formal phrases. Either way what I mean is do you think the more we think about our exams after they are done the more self-doubt we have and generally I should just listen to my thoughts straight after the exam, rather than my thoughts after lost of unnecessary overthinking? (For context I didn't fail, I just want an A* lol)

No offense taken. English is my first language and I am also rather wordy, in part due to my disability.
The more you think about an issue the worse off you will be as know answers can be found. You need to be at peace with the situation and realise it is beyond your ability to control. That should be liberating.