I agree with suzeeq that it's probably row gauge, but I thought I'd chime in since I have such fond memories of making this mistake on multiple projects. (
I've had the row gauge problem before but another time I had to go back and place a stitch marker at each increase before I discovered I had begun the increases later in the pattern than I should have. I'm not sure if it will help in your case, but maybe you could give it a try if you don't think your row gauge is off. It just gives you a different way to stare at a piece you've been staring at for a while.
I was looking at your sleeve schematic and the pattern asks you to start these increases on the first stockinette stitch row after you finish the 2.5" of k1p1 ribbing. So subtract 2.5" from your pre-sleevecap arm length given in the pattern which is 11.5". This gives you just 9" of st st to get your sleeve increases done. Assuming you are working at the stated row gauge of 27 sts/4" consistently up the piece, then you will be knitting 6.75 rows per inch. That should give you just enough room to get all those increases in but if your row gauge is off, then you are probably getting fewer increases in per inch.
Hope you get it sorted!