Rolling from back to tummy

Has anyone else’s LO started rolling from back to tummy when they aren’t great at rolling tummy to back? I put my 20w baby in her cot most days while I shower or try to get stuff sorted around the house, she usually lies there chatting to herself for a while then gets upset so I go and get her or occasionally falls asleep so I get a bit longer to clean etc. On Saturday she’s gone quiet so I assumed she’d fallen asleep so went to check on her (I don’t use the monitor much as the doors open so it’s obvious if she’s upset) and she was lying on her front really struggling to keep her head up. She was near one side of the cot so couldn’t roll that way and had her arm out to the side on the other so couldn’t roll back. I don’t know how long she’d been like that for but she looked tired and wasn’t holding her head high like she does when we start tummy time, maybe she’d have started to cry when it was getting really hard but I dread to think what would’ve happened if I hadn’t gone in then and feel so guilty. She first rolled front to back 4 weeks ago and she’s always a bit shocked when she does, we didn’t do much tummy time before this to be honest, I try to do more now but haven’t been practicing rolling back which maybe I should’ve been? I’m terrified to leave her lying anywhere now (I showered with my phone on the edge of the bath yesterday so I could watch her!) and thought we had ages before she’d roll this way or that if she did she’d be able to roll back. Anyone else in the same position or have any advice?