I felt as if fly like a superman.改错及原因

改成：

I felt as if I flew like a superman.
或：I felt like flying like a superman.

解释：
as if是连词,其后引导从句,而楼主的原句中fly like a superman没有主语,不能算是从句；
如果改用介词like,则其后加名词或动名词也可.