Sleeping on Side

So my daughter was 15 weeks on Friday and the last 2 nights, when we put her to sleep on her back, she’s turned and laid on her side. Now she’s only rolled from tummy to back once like a month ago, so that was just a fluke. I am terrified of sids and of her turning on her belly and not being able to turn back. A few times I’ve caught her turning her face even further and rubbing her nose and face into the bottom of the bassinet. At this age, should I be turning her back on her back? I plan on calling my pediatrician first think Tuesday morning once the holiday weekend is over, but I just need some advice/piece of mind since I’m a ftm.