It sounds like you'll need to import a schedule that matches your league structure. I wouldn't depend on the game to do that for you.
Fortunately for you, there are quite a few schedules that have the set-up you're looking for. The easiest solution would be to import one of the MLB schedules that come with the game.
- Under the Game menu, go to Game Settings;
- Choose League Settings;
- Under Editors, choose Edit League Schedule;
- Under the Actions drop-down menu, choose Import from File;
- Choose an appropriate schedule from among those contained in the OOTP19 Schedules folder.
You can only change the schedule in the pre-season. If you're not satisfied with the schedules that come with the game, you can find other schedules in the schedules sub-forum.