If you reinstall, it is NOT highly likely that you'll see the exact same test - the test is adaptive and has a decent number of questions from which to pull, so it just depends. Still, if you take it again very soon, you'll likely be performing at about the same level, so it's likely you will see some of the same questions.

The real issue is this: if you see more than 2 or 3 questions that you've already seen, and you remember them, this will skew your score higher - not just for those questions, but for other questions b/c you will spend less time on the ones you've seen.

You don't have one great option here, unfortunately. You can try to contact GMAC to see if they can give you any tech support for the issue, but it's a free product so I wouldn't count on that. Your next best option is probably just to re-take the test but, if you do, first review the questions you've done already (and maybe even print screen shots) so you can learn from the ones you've already seen.

I know everyone takes GMATPrep to see their scores but that's really not the best use of these tests anyway. The best use of the tests is to go look at each question, whether you got it right or got it wrong, and learn everything you can, and also to review your broad strategies and pacing for the entire test to make sure you executed in the way you wanted to. The test has a wide standard deviation already and you knew it wasn't an official test as you were taking it - those two things introduce such a wide potential variance in scores that the number spit out at the end is far from the most useful data point here.