Engraving ovals or squares jagged

I have a blue and white 50watt Chinese fleabay engraver, have purchased a couple different rotaries, if I engrave a simple square the left and right edges of square or oval are jagged or crooked, even ones designed in lightburn. they are vector shapes. the sample is on tape but also happens on the powder coat of the mug. Are there some settings I need to change or is this a common issue with laser I have? Again this happens on three different brands of rotaries, but I can cut 3mm wood circles or squares all day perfectly. Seems like it can not engrave the edges on a fill accurately, I have tightened the belts, checked all bolts etc.