If you love it, then don't quit!!!
My quarter inch foot saved me from a lot of headache. And some of the others have suggested different kinds of stops or guides to use on your machine. Those are very, very helpful.
Since you mentioned cutting straight, are you using a rotary cutter, ruler and mat? I find that between those tools and my 1/4 in foot, my quilts are more square and accurate. I can't for the life of me cut with scissors and a template. My mom made all of our quilts that way when I was growing up-- I have no idea how. For me, I'm lost without my rotary cutter.
Honestly, I don't think I'm a very accurate quilter either. I just adjust things as I go. I'll never win a ribbon at a fair, but my quilts are meant to be used, washed and loved. They're going to be less than pristine in the end anyway, so I just do my best, adjust where I need to, and it usually works out in the end. I'm the quilt police's worst offender, I'm pretty sure!!
One time I made this gigantic 4 patch with denim interspersed with cotton fabrics, denim borders and denim backing. Ugh. It was a total mess! I've gotten a lot better since then. Most of my improvements came from trial by error!
I think someone else mentioned trying a different class-- that might change things up enough that you find your passion again and let go of some of the frustration. Different teachers have different talents, and you might learn something new from someone else.
Anyway. Hope that helps! :-) (Really, if you love it, don't quit!!)