MS second shot offer extended!

Just after i booked my exam in im told that M$ have extended the offer 
So what should i do now? cancel the exam, and re-book it with the promotion code or can they just add this when i call the exam booking place? ie prometric

So what should i do now? cancel the exam, and re-book it with the promotion code or can they just add this when i call the exam booking place? ie prometric
Comments
Not that im hoping to fail the first time, i want to pass first time, but the safety net of a second shot aint bad
No wait, I found it...it was the 800-755-EXAM number. Man, to much bottled water.
800-755-3926
Thanks for the help Starter. I ran through the Sybex book summaries and took the test last monday and scored about 50ish points from the minimum passing grade. So now I know what I am weak on and I am ready to go