humm..what is it that you are making? looks like the corner of something to me. you should google how to sew mitered binding. you just use one long piece of fabric all ironed into "binding" and make the edges nice and pretty and folded. but a tutorial would help a lot i'm sure. or you could make tara show you =)
I am a pretty good seamstress if I do say so myself. I agree with Amanda. You want to learn how to do mitered corners and also "stitch in a ditch"!!
Keep working on it, I'm sure it will improve! And even thoug you aren't happy with the seams, I can't even sew at all, so your still ahead of me!