This is the response I got from GMAC:
I do apologize for the issues you are having with the GMAT Prep software.
Your score is displayed in the practice exam right after you complete it. However, there is no current way to get the exam to go back and show you your score after you have clicked pasted it. We currently have put in a request with GMAC to change this feature.
Unfortunately you will have to take the exam again and just be sure not to click past the score at the end. To put your unfinished exam as complete so you can take it again, you will need to start your unfinished exam so that you are at your review screen, once there, click end exam, then click yes to the question that you wish to quit. Once you are back at the main screen, the program will ask you if you wish to save your questions for review, to this click no, and the exam will go into a completed state.