I just checked out the notice for the talk. There's no mention there of black tie, evening dress stuff so I'd suggest just looking good. If you don't have a jacket, try going to Value Village, or some place like that and get the white shirt with epaulets. They usually look very formal, especially with a narrow black tie. Kilts are one of the few exceptions to the black/brown rule. Black shoes are formal when shiny, you should be okay. Just look like you tried.