Related to what others have said, practice riding in a straight line first and keep your head looking up out towards the horizon ( try not to look down at the ground any more than is necessary). Also keep your head straight up and down when you ride ( i.e. don't tip your head over to one side ). Keeping your head vertical means your brain maintains perspective relative to the horizon. You can see MotoGP riders doing this even when cranked right over.

Re-reading your post, I'm also wondering if you might be simply riding too slowly for your experience level.