Forget Paypal for the moment.
Contact the seller. Apologize for your mistake and tell her you only wanted one of the item. Ask her for a Mutual Cancellation of the other four items.
She doesn't have to agree. If she has opened Unpaid Item Disputes she cannot go for the friendlier Mutual Cancellation.
She pays about 20% of the total price to eBay as fees, so she doesn't want to pay without an actual sale.
If you don't pay and Unpaid Item Dispute, you get a Strike which makes it harder to bid on eBay, because most sellers don't want bidders with a record of not paying.
BTW, to order five of them you had to click twice to complete the order. Ten times in all unless you entered the number you wanted of a larger quantity as five. So take some responsibility for your actions. It's tricky to get it all right the first time or so.
