I manage to resolve this issue - it was to do with only having 1 size option - anything over 1 options worked fine

So I used the file from this location - thank you :)

I did have to make a few tweaks to it to get the rows/cols to work correctly though

lines 154 & 155

remove the -1 from 154 $top_rowspan-1
and
remove -1 from 155 $grid_records['H']['options'])-1

all working now :)

Thanks
Sarah