3d fitting surface from data. find function and it's tranverse

Hi

I have data in the excel file.

You can see there Col and Hor results.

and input of two angles. (theta, phi) between -55 to 55 and from -15 to 15.

I used curvefitting and got max polynom till degree of 5. (possible more?)

Next, I wrote a function "find angle from pix dist" that should find the inverse function (get two data points and find the angle) it solves numerically. you can find the polynom in the function.

Still, When i put my data in the polynom I can have a small error that translates to a lare error in the angle. (0.2 degrees for example). I need a max error less than 0.06 degree. don't know the reason i get this assuming the table/ data is correct.

Any idea?