advice on being on top?

so, embarrassing story time:

i've been seeing this guy for a few months, and last weekend we decided to have sex. mind you, i haven't been with anyone else since March, and i haven't been stretching and exercising as often as i used to (y'all know where this is going).

i'm a bigger girl, and he's average weight. when it came time to get on top, i COULDN'T STRETCH MY LEGS ENOUGH. i was so scared of suffocating him too, it was so embarrassing! he didn't seem to mind though, we even laughed it off, but still.

so, please...i need advice! do i need to start stretching a lot more? am i too big? WHAT DO I DO??