As I often tell my girlfriend, it's only a mistake and a waste if you never learn anything from it. Don't worry. In my old 4x5 class, we had all kinds of issues. Some people developed and got superscratched negatives from being rough. Some people got completely clear negatives, for whatever reason (didn't pull the darkslide out, didn't depress the shutter correctly, mixed up the chemical order, etc). Many pulled too hard on the ground glass, and the spring pops off. You need to disassemble the camera to fix it, and by "you" I mean the grumpy older gentleman lab tech that you were always intimidated to go to for help, especially if it was something you messed up.

Shrug it off, and move on to the next shots. Also, never throw a piece of film away, even if it looks like you messed it up. You'd never know what kind of image you'll get off of it! I took a nighttime photo, exposed for over 5 minutes (reciprocity failure), and I didn't get a nice dark negative like I love to see. It was overall clear, with just a few hints of image visible every now and then. My professor convinced me to try to develop it. I stopped the enlarger down a bit and exposed the paper for a very long while, and a decently clear photo came out! It's inconceivable to new students how much data a 4x5 film can store. Many people with developing mistakes, etc. got usable pictures as well.