How do you ride?

Could someone please explain this to me.

I thought I was doing it right but my boyfriend always flips me over and finishes on top. It’s hot don’t get me wrong, but I don’t think that I am doing it right to please him the way he wants.

So my question is, how do you motion your hips to keep him inside of you, but to stroke his entire shaft (9in). I have scoliosis and can’t arch my back to get the full effect.

What are some other positions that require less work for him?