A friend tells me that if you cannot see the mistake from a galloping horse, it won't matter.
Cutting accurately is good, but I had trouble getting a "perfect one quarter inch seam" Someone suggested that I mark one quarter inch left of the needle on my machine with painter's tape. In fact someone else told me to put several layers so that fabric cannot shift by it.
Good luck! It does get easier. And when it gets too easy, you will find a complicated pattern that will stir you to try it!