Hiya,
What's your basis for the grade curve? I see 3 basic approaches
1: Assume the average test score is a "C"
2: Assume the Highest test score is an "A" and work your way down (truly evil prof's may consider the lowest score an "F" and then break up the grades evenly between).
3: Give the class all A's since you smudged your notes (hey that's my vote!)
Hope that helps somewhat,
Adam