Replying to realy realy need some help

I have started to get my 3's dialed now but the only problem is that I have only done them off small jumps outside of the park. I want to try it off like a 20 footer in the park but since I do them on small jumps I wind up and spin realy hard. I've even over rotated on small jumps and done 450's. I'm afraid if I try to spin off something in the park I'll over rotate and die. Does anyone have any advice on how to slow them down?