I need some sex advice

I sort of feel guilty during sex because my boyfriend asks if I can go on top and I try and then I feel uncomfortable or I don’t feel like I’m doing it right and we go back to the same old missionary position. Sure, we both get pleasure out of that but I feel like he’s always doing all the work and I would like to be on top once for him. What can I do? I feel so dumb for feeling so bad about it. He always tells me it’s fine, and he’s always worried about if it feels good for me, but I still feel like I’m disappointing him. Ugh. Help me please!