Is it a sin to say a prayer you don't fully mean?

You are praying in a traditional way as the church taught you...not in a personal way. So you are right. You ask God to forgive specific sin...not general ones. Then "if we confess our sin, He is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness" I John 1:9 It is a good thing to do it daily...but do it specifically...not in a rote, and often meaningless way. And God sees your heart. He knows exactly where you are at when you pray.