on top and hurt his dick?!

so i've only been on top twice and last night i was with someone and he wanted me to go on top and i was hesitant but i did it and i'm not very good at it and so i went on top and i find his dick go in my vagina and when it does and i kinda start moving back a forth and then i stopped cause he said something and he said his dick hurts right it goes in at the tip? wtf i felt bad cause i felt like it was my fault i'm just confused what happened like did i force myself and then his dick flopped? like he was hard . lmao what the hell happened? and how do i make it not happen next time?