Getting the stitches to be even takes a lot of patience, and practise. Try slowing your speed down a bit to med-high.
Start with straight lines until you get that stitch even
Then try gentle curves. Most of us have a tendency to speed up going around in circles or arcs just because it feels smoother that way. Listen to the sound of your machine - if it stays the same when you're stitching. Then you've be able to catch things like speeding up/slowing down.
All you have to do is make sure the speed of the machine remains constant, and you take the time to move the fabric at a consistent speed.