I screwed up, how can I make it right?

I erroneously listed a coin as a Vespasian silver Denarius 79AD in the title of an Ebay auction. The coin looked silver to me and I didn't pay attention but there was an SC on the reverse. I thought SC was only on the senatorial authority bronzes. It was struck by Titus in 80-81 AD.
So I message the buyer, there were two very active bidders on this piece. I say sorry if there was a mistake on the listing, send it back for a full refund if you don't want it. Funny thing is it sold for $200 less that I expected so the buyer must think he got a good deal because he left great feed back but wont return my message.
I sent him a second note to say I'm glad your happy but I made an error. Please let me know if you want to keep the coin or refund it. Again no answer
What do I do now?
So I message the buyer, there were two very active bidders on this piece. I say sorry if there was a mistake on the listing, send it back for a full refund if you don't want it. Funny thing is it sold for $200 less that I expected so the buyer must think he got a good deal because he left great feed back but wont return my message.
I sent him a second note to say I'm glad your happy but I made an error. Please let me know if you want to keep the coin or refund it. Again no answer
What do I do now?

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Comments
Latin American Collection
If the buyer has already left you positive feedback then I would consider the transaction closed and worry about something else.
FOR SALE Items
I've also seen misattributed dates etc...if it's a big mistake I generally send an email so no one gets burned, however to people buying the coins it should be obvious...but sometimes it's on the label of a TPG slab. Once I bought one that was clearly disclosed as a label error by the seller (Hello Jeremy!) and once not, but the values were the same. I just took both slabs to Baltimore and dropped them off at their respective company to get corrected labels.
In any case, my point is that you did the right thing...you contacted the buyer and offered to make good, but at this point presumptively the buyer knew what he was buying and is happy with the purchase. Hopefully there wasn't a big monetary difference.
As others have mentioned, there is a good chance the buyer knew what he was getting anyway, regardless of the title and/or description of the auction. Most people look at the pictures and pay little attention to the rest.