Awwww - I hate when that happens. I don't usually prewash. Unless it's reds, purples, or blacks. And the I use a color grabber sheet. I put it on a low delicate cycle. If I do charm packs (which I probably wouldn't) I'd put them in a small mesh bag of some sort to help keep them from getting tangled. Never prewash strips. Those that do prewash everything usually use pinking sheers to cut along the cut sides - they say that helps on the raveling.
Sorry this happened to you and hope you didn't loose too much of the fabric to use. Guess my advice is only good for the next time you prewash. I do wash everything after the quilt is done.
Hugs