Bad calculus for appointments

Hi there. I have 4 services that are of different time length.
service 1 and service 2 are 45 minutes long and services 3 and 4 are 60 minutes long...
i have a service 3 appointment on Monday at 09:00 (60 minutes long). when i try to chose service 1 and make an appointment, at 9:45 shows that there is a slot available (which is not possible because of the 09:00 appointment which is 60 minutes long). What can i do to solve this? There is only one provider of those services.