Circles arent round

I made a lovely set of coasters as a gift and they came out great except for the fact that they arent round. All I did was make a circle in easel so they should be round however they are all more like ovals. I wanted to investigate further so I milled a straight line on the x and y to see if they make a perfect 90 when they meet and sure enough they didnt. I will add pictures and a video soon but I wanted to get this up as soon as possible.

some info
I have the big xcarve
I did do the strengthening mods
I have the arduino with the gshield

any ideas would be helpful because Im not really sure what could cause this…