My 11 day old turns herself in her sleep. She is placed at the bottom of her bassinet and when I wake up to feed her she is laying diagonally across the middle. Should I prevent this, if so; how?

Some babies do not respond well to swaddling & some like their arms free to touch their face or suck on fingers.
Many of these babies will wriggle & squirm in an attempt to get arms free.

You can try wrapping her with arms out , or you could cease wrapping altogether, if arms free only doesn’t seem to keep baby more settled.
https://rednose.org.au/article/wrapping-babies

Have you started tummy time yet?
How does she go? - if you haven’t been doing tummy time yet, it is important to start.
https://rednose.org.au/downloads/RN0407_22_Tummy-Time.pdf

“Do not use any devices designed to keep baby in a particular sleep position.”
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over
https://rednose.org.au/article/is-it-safe-to-use-products-designed-to-keep-baby-in-a-particular-position

Always continue to place baby on back for sleep.