Linearizing a load cell
If low order 'harmonic distortion' is your main problem, then a low order curve fit is going to give you a big improvement. Two points can only define a straight line, but three will give you a curve, a parabola or circular arc at your choice, but parabola is easier to code, and they're barely distinguishable for small curvature.
It will not improve on any errors generated by changes of temperature, or hysteresis, both of which can be corrected for in other ways. It won't correct for resetability, which is uncorrectable, and looking at the mechanics in kitchen scales I've dismantled, probably quite a significant source of error in cheap load cells.
There's little point to trying to get more accuracy from any curve fitting than the errors of the second paragraph limit you to.