When you created your Fixed Schedule did you select “Specific Days”? With that schedule you can chose any day/s that you want the watering to occur. To change the days you want to water, edit the schedule, click on interval and then select your days.
A fixed even/odd schedule does not let you select days of the week. and the Daily Interval schedule is for when you want every X number of days, so also does not let you select days of the week.