As has been said by many experts here at Beat the GMAT, the number of questions right or wrong is not a reliable gauge of your score - unless you miss very few questions. If you have said you got 3 questions wrong we could expect a very high score, but 12 questions wrong is enough to really influence the difficulty level of the questions that you GOT RIGHT.
Remember the test is essentially trying to decide what level of question with which you are reliable. This is the level of question that you can get correct repeatedly. So you if you see several questions at the 600 level and you get most of them right, essentially the computer will say "okay he can do that level lets move up." And then you have the chance for a higher score.
If you miss questions that at a lower level, say the 500 level, the computer will be giving you questions that are mostly BELOW that level. So you may have missed a few questions that are at the 50th percentile and you spent most of the test just below that level. Yes you got most questions right - 29 out of 41 - but they may have been questions that were around the 50th percentile and below and so you got a 26.
The key to a higher score for you is to get those lower and mid level questions right so that you can see the more difficult questions. Then if you miss 12 you will have a much higher score.
Hope that helps...
