grams = 17.299 volts^2 + 4068.3 volts - 488.45
R^2 = 0.9996
The linear fit is just as good though. I think that this is about as good as your data would allow you to estimate.
The best linear fit that goes through [0.12, 0] is grams = 4129.4 volts - 495.53 with an R^2 of 0.9995