I won an auction P205427806 and paid right away then emailed the seller lizfairycakes@gmail.com and she hasn't replied and I think she's ripped me off what should I do?

Hi Community friends!  Someone is bidding on my auction and they just offered me a really good buy now price. I'm trying to add the buy now though and I'm such a  muppet that I can't figure out how? Any ideas, brains trust? Thanks in advance.