Hello and welcome to the forum,
You don't tell if the pretest was created with the default pretest question slides? If yes you have to use the system variables available for pretests. Have a look at:
http://blog.lilybiri.com/system-variables-in-captivate-6
To create a custom results slide, maybe this post can help you:
http://blog.lilybiri.com/intermediate-score-slides
Lilybiri