So last night, our party's wizard casted on himself true strike, so his next round's scorching ray would be a direct hit. He rolled on his round and rolled a natural 20. So It was a threat. My question is if the true strike counts towoards beating critical confirmation ac. (Would his roll still be +20)?
Yes, because confirmation has the same modifiers as attack (all pluses and minuses).
As written in SRD: