Contact the seller.
Most sellers would rather cancel an unhappy unpaid transaction than go to the trouble of an Unpaid Item Dispute, which also gives her back her selling fees (it costs money to sell here) and hits you with a Strike that would make it harder to bid on eBay in future.
Be aware that the seller may add you to her Blocked Bidder List.
Usually here I add a note about asking questions BEFORE bidding, but with your experience, that would just be embarrassing.
