Extract the polynomial? I think you mean approximate your data using a polynomial. You cannot model your data perfectly using a polynomial, because your data is rough and not smooth while a polynomial is a perfect mathematical curve, so you are just telling excel to try and find a polynomial that fits your data as closely as possible. Here the coefficient of determination for the polynomial

is

which means it is a very good (almost perfect, in fact) approximation of your data.

At least that's what I understand from your question. Feel free to clarify if I missed your point.