When you are using the autoscheduler, the field can only be used as one size. You need to decide whether you want to use the field as two 9v9s or one 11v11 field.

What you can do if you'd like, is make the full size field unavailable, run the autoscheduler, and if there is space left, you can manually place a game or two on the full sized field after the autoscheduler is done.