It sounds to me like you're supposed to end up with 2 1/2" of garter stitch total, as opposed to 2 1/2" from where that line appears in the pattern. Hard to tell for sure without the whole pattern, though. If it's a free pattern available on the web, could you post a link?
Yes, ws means wrong side. Technically there is no wrong side in garter stitch, but there may be a wrong side of your pattern. Again, hard to tell without seeing the pattern. You may be able to tell by rereading the beginning part of the pattern.