Everyone has insecurities. It's normal to have them. If you are having these negative thoughts, then you might as well just try and remove them off your mind. Again, as many other have said, validations of your feelings is important but it won't give you the confidence you need. Do you know the reason why you are thinking this way? It's important to know where these feelings are coming from so you can know how to get rid of them. Sometimesnegative thoughts isn't about how you feel now but a repitition of how you felt once in the past. Try to distract yourself with stuff that can help with your self-care and that can get you out of your cycle of negative thoughts. The reality is that insecurity is not just for teenagers or young adults but also, sometimes the gold medal winners are the most vulnerable of all, because they rely on exterior things to reassure them of their place. Finally, do not ever compare yourself with others, just focus on yourself. We can't force you to feel better about yourself, it's something you can decide by yourself.
When you have negative thoughts and beliefs, have you tried distracting yourself in order to feel better rather than examining them? Research and experience suggest that disengaging from your negative thoughts gives the ego's negative self-talk less power. It allows us to chill out and gain control over these intrusive thoughts and belief systems, not letting them lower your self-esteem.
Now, don’t get me wrong, this is a much different concept than avoiding. Avoiding is pushing something away and trying to forget it happened. Avoidan-ce can be the cause for much future distress and suffocates your ability to work through problems. Distracting is temporary; it gets you to a place where you can think in a more skillful, logical manner. Getting out of your head is a great way to move forward. He invited you to a party and you want to be confident, my advice is to just be yourself. Also just out of curiousity, how old are you?