Dear Let say your file name is "someFile.xls" then following code should work.
[m mess] = xlsread('someFile.xls', 1);
The size of mess with be number columns and rows in sheet one. Lets assume that in first row second colum there is your requires string you want to take first three initial characters. Then this code should work.
a = char(mess(1,2));
myStr = a(1:3);
Try and let us know, if it works. For experiments you make your own xls file so that you put the string you want. Once the code works and give desired resutls then it would be easy for you to debug your problem in your current xls file, as you mentioned due to spaces or anything.