You are adding 2 days of 30 minutes of exercise, so you are adding more time to your goals, so your calories burned goal will increase like you are seeing.
As for setting specific days that you'll do certain things, there isn't a way to do that. We recently updated the fitness tracker page and that is no longer an option. To learn more about the update to the fitness tracker, you may want to view this page: www.sparkpeople.com/mypage_public_journal_
Hope that helps!