Best advice - if you make a mistake, make another one just like it and say it's suppose to be that way - heard Liz Porter say this.
If an instructor ticks me off, I don't take a class from them again. A few years back I signed up for a quilt as you go class and bought all my supplies and precut the batting. She was extremely upset with me over the poor quality of my batting. All the supply list said was batting. I was new. Good grief, when I was a kid we bought wool blankets from the Salvation Army and that was our batting. We used old cotton sheets for foundation strip piecing.
I say, if someone gets real snooty, tell them to go to a quilt museum, like the one in Paducah, and look at the quilts made more than 50 years ago. You will find that the points don't match, some seams are crooked, mixed fabrics because they used the good pieces of worn out clothing. Yet, all these quilts are beautiful.
So, my advice is, don't stress on the small stuff and enjoy quilting. Now a days when I take a quilt class, I don't argue with the instructor, I learn new stuff, if I don't like a certain procedure, I don't do it that way, I find a way I'm comfortable with.