When you are preparing to take the actual GED test, remember to get plenty of sleep the night before. If you work third shift, you may want to arrange to have a day off. Each of the battery of the GED tests is long.... not short. You will need ALL your mind energy!
Eat a healthy well-balanced meal for breakfast! The last thing you need on your mind is a grumbling stomach! Eat something.... even if you need to grab an apple.
Don't do any last minute cramming... it is better to have a rested and relaxed mind. You have done all your studying already, so just go in and do the best that you can.
Good luck and let me know how you did!