adding data to an existing excel file

Hi,

I have the following script. I want to write the "data" from 36 folders to be written in one excel file, one at a time. For example, the first piece of data be written in columns A,B, and C. The second piece of data be written in columns D, E, and F, etc. How should I change the script? I thank you in advance.

       clc, clear, close all;
       STIMroot='C:\Users\';
       Drop=strcat('C:\Users\final.xls');

        for i=1:36
            for j=1:2               
                for h=1:29
                   STIMfile=strcat(STIMroot,num2str(i),'\',num2str(i),'_',num2str(j),'_',num2str(h),'.xls');

                    if exist(STIMfile,'file')
                    STIMdata = xlsread(STIMfile); 
                    data=STIMdata(:,3:5);

                    m=1;
                    [rows,cols] = size(data);
                    startingcolumn = (m-1)*cols + 1;
                    colsstring = num2str(startingcolumn);
                    m=m+1;
                    xlswrite(Drop,data,1,colsstring);

               end
          end                                    
    end
 end