Unable to require scheduling on the :00 and :30

I'm trying to allow clients to schedule 45 minute appointments that can start every half hour (based on my existing availability).

I've set business hours as 9 - 5, time increments of 30 minutes, duration of 45 minutes with a 15 minute buffer after.

The result: I start the day properly with 9:00, 9:30, 10:00 time slots until there's a meeting in my calendar that doesn't end on the half hour, and then booking availability shows as 1:55pm, 2:25pm, etc. Is there a way to keep it to the :00 and :30?