The title was a bit confusing, perhaps that was the intend.

I mean to question something that you are sure yet you are not...

I mean, when I read the poem I thought that perhaps, indeed, you are sure that you are doing it right because you feel relief and cleaned after praying, however, there are doubts on whether the praying is done properly?. And I'm guessing that's where the title comes from.

"I do know if I do it right?"

My first thought when I read it, I though it said I don't know if I do it right? But then I can see why is I Do Know if I do it right? You are not entirely sure, yet you are.