Your row gauge may be different than in the pattern. It seems you did inc on every 6th row, which should be Rows 1, 7, 13, 20 and so on. What does it say to do after you reach the 11½" from the beginning? If it's just to work even until sleeve is X" long, and do the underarm/armhole shaping then you're probably okay. I'd say if it's the right number of stitches, then the increase rate may not matter. If you want to clip the sides together and try on the sleeve to see how it fits, that may reassure you. It may be you need the extra half inch in length anyway, I would. You can deviate from the pattern a little as long as it comes out the right size.
eta - I found the pattern http://www.lionbrand.com/patterns/90186AD.html
and on ravelry at http://www.ravelry.com/patterns/libr...assic-pullover
11½" sleeves are ridiculously short. I know this is an oversize sweater, which would mean the shoulders are wider so the sleeves don't need to be as long, but they're practically the same length in all sizes. That's not correct. I'd say to pin the sleeves to the underarm of the sweater body then hold it up to you and see if they're too long. If they are, then check your row gauge - the pattern says 27 rows = 4 in which is almost 7 rows per inch. You could rip them back about halfway and change the inc rate to every 4 rows and when you get to 72 stitches they should be a few inches shorter. If they're still longer than 12", then you might skip the last couple of incs and go for 68 sts and do less decreasing on the sleeve cap, which may happen anyway because if your row gauge is off that much, the cap is going to be too long anyway. But then you should end up with the 10 sts sooner so it may fit the armhole.