I added up my mastery score myself, just by scrolling through my collection and mousing over each one, and it's approximately 5 levels higher than what is being displayed on my profile. Is there any way to fix this? I can't really show you my mastery level on each individual champ, I'm just hoping there's something you can do.
Is it possible you were filtering out champions you don't own, and you have levels on some champions as they were free?
That... may be a possibility. Usually I ignore the free champ rotation though, because I play ranked so much. If I was counting any freebies, I'll find out. Soon enough. After this game. 
:D
Yeah I definitely didn't accidentally factor in any free champions, I only play champs that I own. I double-checked just in case. Lost that game btw, still went 13-5-11.
