Minimalist Cardigan -- need advice

So I've been working on the Minimalist Cardigan for a shamefully long time now. The truth is, I've gotten stuck: I'm not sure I'm going to have enough yarn for the sleeves to be as long as I want them. I've put up a notice on the ISO/Destash group at Ravelry, but no one's bitten yet (I may get desperate and take a different dye lot -- Brown Sheep Lamb's Pride does tend to be pretty color-reliable from lot to lot). I have been trying to get everything done on the body, including seaming as much as I can, before actually deciding that I need to buy more yarn.

I have another issue with the cardi that is more pressing, though. After steam-blocking the fronts and back -- and kitchenering the two front pieces together* -- it appears that the back is significantly larger than the front. The pieces aren't matching up at the shoulder in any kind of logical way. There's about a three-inch difference, which seems like it's probably too much to fudge where the sleeves are set-in.

What to do? I knit and re-knit the darn back about three times, and would really prefer not to have to frog it -- but if that's what I have to do, I will. Reknitting the back so it's smaller would, after all, mean that I'd have more yarn for the sleeves, and then I wouldn't have to worry about that as much. But I also don't want to have to do any math to figure out how many stitches I should have at the top of the shoulder (um, that's why I used a pattern in the first place: someone has already done the math for me).

I could also undo the kitchener stitch seam and knit a few more inches into the neckband until it's the right size, and then re-kitchener the stitches. But I think the fronts are a good size, and I'm reluctant to do anything that would make the shoulders of the sweater bigger. I like set-in sleeves on me, not drop-shoulder sleeves. I have smallish shoulders, and if my clothes fit too big in the shoulders then you can't tell how slim and cute I really am!

So: help? What should I do?

*Funny story about that kitchener stitch. I went to first-Saturday knitting at Mango's house and spent all afternoon struggling with it. I'm generally not one of those people for whom kitchener stitch is a problem, but I just was NOT GETTING IT that day. And since the only other project I'd brought with me was also a seaming project, it wasn't like just working on something else was really going to be an option. I probably spent three hours hunched over this one seam, and when I left her house I had gotten exactly half of it done. Three hours, for two inches of decent-looking kitchener stitch and two more inches to go. UGH. I went home, finished up some things for Sunday morning, went to bed... got up Sunday, worked all day, grabbed some dinner out, came home to settle in to the Oscars red carpet show... and did the rest of the kitchener seam with no problem. The half-hour red carpet show took longer than the seaming. Sigh. There is a funny shadow in this picture, darnit, so you kind of can see where the seam is, but when you're looking at the piece itself you can't see a thing.