You've probably gotten to the end of a tough level, grabbed all the gold, the pluses and all you have to do now is nail that bullseye.... but then you miss.

If you're having trouble, I've setup a simple AutoHotKey script that should get you the bullseye each time. Just hit F1 the moment you cross over the left side of the blue cannon platform and get that bullseye.

The timing can be a little tight so you may have to just get used to it, but it should be a bit easier to get than trying to gauge it yourself.