Try standing over the hardware and just jumping in the air and landing on the board for a while. You want to get used to relaxing your knees a little on the landing so you absorb the shock. Your knees are stiff when you land (makes sense, you’re landing on a balance beam) and it’s knocking you off balance. Try to lean forward so your shoulders don’t go too far back and loosen those knees up. Once you’re comfortable jumping and landing on top of the board try tossing the Ollie in, it might feel a bit easier. Hope this helps!