Hypothetical case: I have been putting tefillin on every applicable morning for many years now. This morning, in shul, someone came up to me and said, "Your shel yad is placed completely incorrectly! You haven't been putting tefillin on properly at all." He then showed me sources and diagrams with arrows and descriptions on the back of each one and lo and behold, he is right! I was never formally taught and, though I copied others, I guess I copied wrong, thinking I was doing it right.
Do I get any schar for having had the intention to perform the mitzvah properly or is it as if I did nothing and I made a bracha levatalah each morning?