You are not your code, even though a lot of people will try and convince you otherwise, EVEN YOU!
Just write shit that makes you happy, side projects are about exploring and having fun.
Often times the negative Nancy voice is right when he is talking to me. I often don't know what I am doing, I write horrible stuff all the time that does not work!
Realize this though, you are in control. Whenever those thoughts appear you actually have a choice, listen to them or say no.
By listening to them you will never get anywhere, you will constantly second guess yourself and tweak minor details that can be changed easily at a later time. Your free time is limited, you have to cut corners to see significant progress. Once you realize that everything is a compromise, it gets easier.