CNLS (complex non-linear regression least square) Method, goodness of fit and chi square.

i have acquired one plot from one of my system, to analyze the graph and extract the parameters i need to curve-fit it through one of the algorithm of regression.
it can easily be seen in the plot, the fitted one and the original one. now i have acquire the x and y points for the fitted one and i already have the original one's as can be seen in the points table. what i want to do now is to find out the error in between both the plots something like Chi-square and find out out goodness of plot in percentage that how good it is fitted.
keeping in mind i am very beginner in the statistics and probability.
thanks in advance.