Ebay help - totally messed up

[Missunreasonable]

I made an offer on a buy it now / best offer item. The offer was accepted and I confirmed it and then I realised that I had missed something very obvious on the listing and that item wasn't what I thought it was. I had already contacted the seller asking to send an invoice but I re-contacted them immediately asking them to cancel the transaction and apologising profusely.
I feel terrible. I have never had any problems with ebay transactions before . It is quite an expensive item and I cannot afford to buy it and then buy the one I actually need as well.
What will happen if the seller won't agree to cancel the transaction?
I hate messing people about.

What might help is if you offer to cover the costs of relisting it so that the seller doesn't miss out.

Yes, I can do that. How much would it cost?

It was a trader, I don't know if that affects listing costs or not.
I feel such an idiot.

Think I might have done this too. mine was because I'd read so many already and presumed the title bit was correct and thought I'd read the details of the description already. Waiting on hearing from my seller. In my defense when I did read the description (after purchase) it wasn't very clear.

I feel really stupid but I am sure that lots of people make genuine mistakes on ebay. Fingers crossed that both of us get a good outcome.

I would not offer the relisting fees as once the transaction has been cancelled the seller will automatically get back his fees which will cover the relisting of the item.

People do make mistakes on ebay and most sellers will be fine with cancelling :)

Thanks bats this is the first time I have asked a seller to cancel and I have made hundreds of purchases.

there is absolutely no need to offer any relisting fees as there will not be any. Ask the seller to cancel to get their fees back, they can relist for free and that will be that.

Panic over. The seller has cancelled the transaction and relisted. Thanks everyone for reassuring me that this wasn't that unusual for an ebay situation.