More rotary problems!

Another rotary problem: my image on a cup is skewed. I’ve had to adjust the image (a circle) to 72 by 82mm to resemble a circle. My steps are correct 2970, and after burning 25 cups, my laser is starting the skew or it looks like the cup is slipping when I watch it that doesn’t seem to be the case. Below are some pics- I have a 80 watt red and black Chinese laser. Had it for a whole month so I am pretty sure it’s operator error. I did put a line in front of the image at 2% power to try and avoid skewing the image. Any help is greatly appreciated!!