Hi, my 3-week old was born breech and sleeps with her legs stretched out, which makes her roll from her back to her side immediately. I tried rolling her back but she will just keep going on her side. What can I do to fix this as I’m very worried. Thanks

It is not unusual for babies to wriggle, roll to side or move around their sleep environment before they are rolling.
Are you swaddling/wrapping your baby?
Some babies do not respond well to wrapping & may wriggle to attempt to get out of the wrap/swaddle.
Some babies like to touch their face or suck their fingers.
She may or may not be rolling to her side because of she was born breech.

You could try wrapping her with her arms out.
It is important that baby’s head & face remain uncovered & as you are doing, always place baby on the back for sleep.

How does she go with tummy time when awake?

Red Nose does not recommend the use of sleep positioners or anything that restrains a baby in a specific position.
https://rednose.com.au/article/is-it-safe-to-use-products-designed-to-keep-baby-in-a-particular-position