STEVEN IS NOT GOING TO BE CORRUPTED!!!!
If you see how small Jasper is, than see her corruption, it seems that the corruption is 2x bigger than the gem's size.
Then, look at Pink. Pink is small, but if she were to become corrupted, she would not be as big as the big worm.
Since I saw a theory about the pink white Diamond being Jasper and White Diamond's fusion, the worm could be Jasper and White Diamond's fusion.
Jasper and White Diamond's Fusion is (probably) half the size of the worm. And, one more hint, Jasper has horns, while the worm does has horns too.
If you see the Pink White Diamond, her nose looks like Jasper's gem too. Then, look at her attire, it looks like Jasper's.