To get the name inserted rather than the id you would just need to adjust the dynamic properties of the select list so that both the label and value were referencing the same column from your category table. What do you currently have for the values of this category select list?
As a way of testing the query that is being executed you can add in a die statement to print out the sql. Find the $WA_Sql variable that holds the query toward the bottom of the insert server behavior. Add in a new line after this and add the die statement like this:
You can examine the sql for problems, if you don't see any you can post it back here so others can take a look and try to find any problems.