I found out a while ago that when you do ghusul, after washing the head and neck you have to get out of the the stream of water and then wash the rest of your body. Before I found out about that ruling, I don’t know if I did that in my previous ghusuls. Do I need to make up my prayers and fasts?

Rather you cannot stand under the water and move your body parts for ghusl. It is essential to pour water on the body parts either with a jug, or by moving the shower head over the body parts or, using ones hands to make sure the water reaches all the parts of the body

Q19: What is the ruling on a person who used to pray and fast but committed several mistakes in the major ablution (ghusl). He is absolutely sure now that some of his previous ghusls were void, but he does not know how many. As a result he is not aware of how many invalid prayers and fasts he offered with them.

A: His fasts are valid even if his ghusl is invalid. However, it is obligatory for him to offer qada of all the prayers he offered with the invalid ghusl. If he is unsure about the minimum and the maximum, he may limit himself to the minimum. (FM, p. 399)