Send an email through Contact Buyer stating that, given your errors in the description, that you are willing to do a Mutual Cancellation on the transaction. Tell the buyer that this will free both of you from the transaction with no repercussions.
Both of you can leave feedback with a Mutual Cancellation. You will get your selling fees back.
If the buyer is being grouchy, do NOT offer the MC, instead wait until 4 days (96 hours) have passed without payment and open an Unpaid Item Dispute. With any luck, the buyer will not pay. Fingers crossed. Close the Dispute after another 96 hours.
The buyer gets a Strike, which is not entirely fair since the description errors were yours. However, he cannot leave feedback either, which may be more important to you.
Keep it polite and professional. Mistakes happen.