My son is a little over 7 months and he still will not roll over?

I’ve seen him do it before a few times on his own front to back, and back to front so i know he CAN do it, but he just won’t. i lay him on the bed multiple times a day so it’s soft for him and he tries so hard but he ends up just scooting himself around the bed instead.

I just thought once they’d done it a few times they would just know how to do it…

Also i see babies his age online thay are now crawling around and it makes me anxious because he is not crawling and i wonder if he’s behind because he’s not rolling 😔 i feel like i’ve done it all wrong

at his last appointment at 6 months doctor wasn’t too worried since he hits milestones and he was trying to roll, but another month has passed so i’m more worried…

Advice?

Thanks in advance :)