Rotary settings help please

I have c3d mini and c3d rotary running lightburn
My issue I’m having is the rotary spins a little too far.
I have an 80mm acrylic tube which equals 251.3mm
But it goes a little further than that.

and my circles come out oblong/oval. My delta steps are 17.77. I’m only running 10mm sec
What adjustments can I make?