You're not supposed to finish all the questions. It's all about accuracy, speed, paying attention, doing your best and just getting through what you can. If you finish all the spec test questions in the time, you would be some sort of freak in my opinion (and deserving of respect for your mathematical skills!).
Just relax, be yourself, be confident without being arrogant, express yourself clearly without making excuses, look the recruiting officer in the eye and think about your answers before running your mouth off. Give enough detail to answer the question but not so much they'll get sick of hearing you talk.
Let us know how you get on!
