So you accepted a reservation, then decided you'd rather cancel so you could make more money?
That's not cool - you made an agreement that you're backing out on, so they've blocked the dates & you won't be eligible for SuperHost status for 1 year. If you cancel for no good reason a couple more times they'll start charging you for it. They really penalize that kind of behavior because it gives Airbnb a bad reputation. (I'm glad they do - I want my guests to know I'll do everything I can to follow through when they've made a reservation with me)
You could try booking through another site for that time period.
In the future, be sure to keep your calendar updated - don't open it any further out than you know you can host - and don't go back on your agreements.