Well, without code to look at, it's hard to point out what may have done wrong -- a simple test here worked just fine...
p=[20 20 210 80];
hUIF=uifigure('Position',p);
hUIT=uitable(hUIF,'Position',p,'Data',[129640 pi],'ColumnName',{'x','y'},'ColumnWidth',{60 120});
hUIT.ColumnFormat={'short','long'};
Changing the 'ColumnWidth', 'ColumnFormat' properties modifies the table as expected. NOTA BENE: the formatting options aren't very extensive, one of the values recognized by the format function or just one of {'char','logical','numeric'}, ignoring the pop-up menu thingie. Unfortunately, as with the builtin table, setting a specific format string for a given variable/column isn't supported; to do that you'd have to display everything as text and use callback function to format and then display the value.
