[Lisa~]

You round your back slightly during your pull off the floor. That's probably where the back soreness is coming from.

Point your toes straight ahead during the RDL. There's no need to toe out since you're not pushing against any hip mobility issues for this lift.

You're bending your knees too much. After about a 10 degree knee bend at the top of the movement, stop bending at the knees and focus only on shifting the hips back. You shouldn't have to put the bar out and over your knees. It should travel straight down and your lower legs should remain completely vertical with no forward travel at all. You achieve this by putting your hips further back.

Your low back position during the set was fine.

Finish with a hard contraction of your glutes into the bar (f*** the bar).