hmmm i've got naturally neat writing. I was the first person in the grade in year 3 to get a pen license! lol.
I find that whilst i write quite neat in exams, it really depends on the type of pen i have. I got this new one called Dr Grip by Pilot (though it cost $15) and it requires less grip, money back guarrantee, so i can write more without my hand getting sore, meaning it's neater. I also found in the half yearly's i had a pen which totally flowed, and because it wrote so easily i wrote better.
So if you're out of time and desperate, play around with different pens and different grips... it might make that little bit of difference.
Alternatively, if you still have the time, there's a coaching clinic in Hornsby which deals with handwriting. They look at the way you sit, the pen you use, the grip you use etc and fix it up. They're supposed to work miracles, however are quite expensive. (i don't know what they're called or their phone number or anythign - might have to ask around. I heard about it from my english teacher.)
Good luck!