To things to remember when trying this:
1. Carve into it slightly
2. Just as your coming off the jump turn your whole upper body as if you are immediately looking for the landing before you even cna see it. This will also keep you from over spinning.
This is hard to tell what your doing wrong without a video. But look at Snowboard Addictions videos about spinning and look at how they do the run up to the jump. Best way to come up to it. Remember the time glass picture. Which way are you spinning too?