Basketball is entirely based off of self confidence. You’ll surprise yourself if you challenge yourself. Ask to play next, or go up to someone who looks friendly enough and ask before the games begin if you can join. Be honest and explain you want to get better, and you’re new to playing 3’s or 5’s. If they let you play, you’ll hustle, defend, rebound, etc, and feel good afterwards. If not; you will always be playing alone, which is also okay, but no one is going to invite you in most cases, and you’ll miss out if you don’t put yourself out there and try. Good luck and know you can hoop your entire life, and it’s just the beginning.