Is not doing National Guard when you had the chance going to be on your concience?
Can you justify missing the fun you'll have there before you get stuck forever in boring civvy street?
Sounds like an obvious choice to me.
If I was an employer I'd actively look for the qualities of dedication, ability and commitment that an NG history demonstrates.
As an employee do you really want to work for the sort of company that sees a NG commitment as a negative factor????
Go do it, enjoy every minute of it, and settle for a boring quiet retirement. At least your early career won't have been boring and quiet, unlike most of your oppos...