I'm having trouble sighting my scope.?

I have a crosman quest 1000 with a scope from a crosman quest 1000x. The scope is 4X32 and has worked on a air rifle gun that shoots BBs and 375 fps. Now my crosman is 1000 fps and i started sighting maybe around 14 ft away from my target. It kept going wayyy down and i adjusted it so high that it maxed out and still ended up down. What am I doing wrong?