How can I get this guy to ask me out?

The best is to give him a clear sign. You want something quite precise from him, so take action in his direction: give him a call and see how he responds to your contact.

If he feels open, try to make a date, something fun to do together and see from there.

I would not focus on that single event.

The best is to simply get closer to him and feel how he reacts.

Enjoy!