You are getting the column widths correctly, placing them in a new datarow in a new datatable but you are not persisting the information between sessions(every time you start debug).
What you need to do is PERSIST the data, if you won't use a database then you need to write it to the local users hard drive. Then when the session starts READ that information and format the column widths. I would not use the index as the user may be able to reorder the columns.
Here is an
article [
^]where I store and read the forms states.