I draw my 1's the way it's often displayed on screen, with a little tail at the top and a line at the base. Your system keeps detecting this as a 2. I've also had 3's detected as 2's.
I have always written 1's with a tail at the top. That is both the way it's taught in German schools, and how this program outputs the digit. Most of my attempts get recongnized as 7.
I prefer my writing as unambiguous as possible, so I also like that way of writing it. Like someone else mentioned, "mousewritten" is not necessarily the same as handwritten, so that could be part of the problem.