Provisional Cast-On ~~ can't get it

[knitqueen]

I've been trying to do a provisional cast on for this pattern. It all makes sense to me and I think I get HOW to do it, but something just isn't coming out right. The pattern is to cast on 17 stitches, and theoretically I should then have 17 stitches also on the spare yarn that I'm using for the cast-on. But no matter how I do it or how many times I try, I end up with only 16. So obviously once I'm done and go to kitchener stitch the two ends together, it won't come out right because the # of stitches isn't the same on both ends.

Help anyone??