Gizmo had one ear up very quickly and it seemed like it took forever before the other one stood up but it finally did and I kept the tips of his ears shaved all the time. I dont think you have anything to worry about. In the event it doesnt stand up..your baby will still be cuter than ever! I think one up and one down is just soo cute!
Oh and I havent ever heard of any balance problems associated with one up and one down so no worries there either!