My 10 week old is currently sleeping in a bassinet in a sleeping bag with his arms in. He is starting to move around a lot during his nighttime sleeps, we wake up and he has moved himself to being completely horizontal at the bottom of the bassinet or diagonal with his face against the edge. He twists and turns a lot too. Is this safe? Im worried he is going to roll over. He is rolling from tummy to back consistently during tummy time.

Most babies do not roll to tummy intentionally before 3 months; however, some babies do roll, especially to the side or other parts the cot, at a very early age. This is not unusual.
There is no need to stop your baby from wriggling & changing his position, but it is important to make his environment safe as he is moving a lot & rolling during tummy time.
He will no doubt be rolling when sleeping soon.

Most babies will be rolling over by 4-5 months…....some earlier, some later.
This is very normal as babies grow & become stronger many babies then prefer to sleep on their tummy &/or side.
Once rolling or attempting to roll the following is important:
*Time to stop swaddling/wrapping.
*It is important that you move him from bassinet to his cot.
*Baby needs arms free & the space of the cot to roll safely.

Continue to place baby on the back to sleep.
Ensure cot mattress is firm, well-fitting & flat.
Ensure there is nothing loose or soft in the cot.
Preferable to use a sleeping bag when rolling that has appropriate size neck & arm holes, rather than swaddle.

Red Nose has the following information when baby is rolling.
Give baby extra tummy time to play when awake and supervised as this helps baby to develop stronger neck and upper body muscles which in turn enables them to roll back over.
Make sure that baby is on a firm and well-fitting mattress that is flat (not tilted or elevated).
Make sure that baby’s face and head remains uncovered (do not use lambswool, doonas, pillows, cot bumpers or soft toys)

As babies grow and develop they become very active and learn to roll around the cot.
At this time, continue to put them on the back at the start of sleep time, but let them find their own position of comfort.
By this stage it is not necessary to wake during the night to turn baby over to the back position

*Do not use any devices designed to keep baby in a particular sleep position.
https://rednose.com.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over