Dang It!

I just discovered the crappiest thing. The really cute patterns that I bought for pj pants for the girls are the wrong size. One of them will fit Laynie, but one is still too small for her and neither pattern is big enough for Kassi. It's my own fault, really. I guess I was caught up in the giant sale craze at Jo-Ann's, and in a hurry, and just not paying very good attention, all which are normal for me, but dang it! I was so looking forward to getting started on those pj's! So I guess I now have two options. Option 1: Try to return the completely wrong size pattern and keep the pattern that will fit one child. Or, Option 2: I can attempt to "resize" the pattern to fit my girls. It seems to me that for every 1/2 inch that the size increases, the pattern piece also gets 1/2 bigger, with the exception of the fold for the waist elastic and the hems. These also increase proportionally. So, is it possible? Could I just measure out the required 1/2 inch (or whatever) and follow the line of the smaller pattern? Can I actually resize the pattern? I don't know. Feedback would be greatly appreciated here, I really like the pattern itself and I am itching to start these pants. I would hate to have to wait two weeks until I can get back to Jo-Ann's to find out if they will even let me exchange the pattern. Help!