put together a practice (sandwich-some people use 12" blocks) and do some practicing- you have to coordinate your (foot speed) with the speed of the fabric/stitch- it takes some practice- it is always a good idea to practice on something (just 2 pieces of fabric with some batting in the middle works) before 'attacking' your actual project- but you can not expect perfection---it will not be perfect- people who have been doing it for years still have on occassion- some uneven stitches---
if the stitches are very tiny- you are stitching faster than moving the fabric- if the stitches are big you are moving the fabric faster than the machine is going- it takes time to find a (rhythm)
don't be so hard on yourself- when you go back to class you will find everyone will have some areas that are not perfect-
i've seen some with stitch regulators- that still on occassion have the same problem-
it certainly does not mean you are not meant to do this- it just takes time/practice and patience.
if you use a thread that blends in to the fabrics- the little areas that are slightly bigger/smaller---are not going to be noticable- and no one is going to be there with a ruler measuring your stitches
if you find the tiny stitches are the biggest problem you could try increasing your stitch length on the machine- but it really just takes some practicing ... and not expecting it to look as if it came from jc penneys- all hand work has variations---the difference between doing something yourself-and buying something manufactured---don't be so hard on yourself- or expect perfection---we strive for perfection- we never really achieve perfection