Im sure you'll do fine
Rest and relaxing cant do any harm, have a hot bath the night before, get a good nights sleep, eat a light meal before the grading and give it a couple of hours to digest. Do a good warm up and listen to what your body is telling you. Most importantly, have a good positive attitude.
Get up and have fun. Look like your enjoying your aikido but also as if nothing bothers you. Remember, the panel is wanting to see you make a mistake so they can see how you deal with it. Just switch to another technique and keep going if something goes wrong.
Tell us how it goes!