Sex advice pleaseeee!

Ok, so me and my boy friend have been together for about 3 months now & we do have a active sex life together. Ever since maybe like about maybe 3 weeks ago he's been asking me to get on top and ride him while having sex, & I'm not saying I won't do it I don't have a problem with it at all but i feel like I'm too big. & I guess I'm just asking like how should I go about doing it cause I kinda want to do it also.