Appending Values to a Table

Menu "Macros"
"2D Guassian Fit...", My2DGaussianFit()
End
Function My2DGaussianFit()
    Variable L, H
    Variable ii
    Prompt L, "Enter Lowest Tw Value:"
    Prompt H, "Enter Highest Tw Value:"
    Variable xmin, xmax, ymin, ymax
    Prompt xmin, "Enter xmin value: " // Set prompt for x param
    Prompt xmax, "Enter xmax value: " // Set prompt for x param
    Prompt ymin, "Enter ymin value: " // Set prompt for y param
    Prompt ymax, "Enter ymax value: " // Set prompt for y param
    DoPrompt "Enter Parameters", L, H, xmin, xmax, ymin, ymax
    if  (V_Flag)
    return -1 // User canceled
    endif
    for  (ii=0; ii<(H); ii+=500)
        string  waveselection= "avg" + num2str(L+ii)
        Wave ws= $waveselection
        Wave w1
        Wave w3
       
        Display; AppendMatrixContour ws vs {w1,w3}
            ModifyContour $waveselection labels=0
            ModifyContour $waveselection autoLevels={*,*,35}
        CurveFit/NTHR=0 Gauss2D ws[xmin,xmax][ymin,ymax] /X=w1[xmin,xmax] /Y=w3[ymin,ymax] /D
            wave W_coef
       
            Variable integral
           
            if  (waveExists (W_coef))
           
            integral= W_coef[1]*2*pi* W_coef[3]*W_coef[5]*sqrt(1-W_coef[6]^2)
           
            Print integral
            endif
    endfor
End