One bad game and I start questioning whether I'm ready for adult football

The first thing is to separate a bad opening spell from a verdict on whether you belong at the level. Young players often make that link far too quickly. After two or three mistakes, reduce the next objective. Do not try to repair the game with a brilliant pass. Find one simple action you can control: show for the ball, play a secure pass, recover into position, compete for the next second ball. That gives you something current to judge yourself on instead of replaying what already happened. It also helps to expect mistakes before the game. Adult football will expose you differently while you adjust, and that is part of learning it. The aim is not to become a player who never gives the ball away; it is to become one who stays available and useful immediately afterwards.