double booking for one service provider/multiple services

I'm working as the only service provider for my business. I have 4 service options that are available for the same days/hours. But only one service can be performed at a time, since it's only me! However, when a client books service A at 5pm on Monday, Service B, C and D are still available at the same time. How am I going to prevent double bookings? Did I miss a setting?