Ebay estimated shipping for listing was less than half the actual cost

[bylo-selhai]

Apparently I was a fool to let Ebay estimate the shipping for my item. Ebay recognized the item from the title and estimated USPS shipping at $17.20, but when I tried to ship the item I learned that the real cost for the cheapest USPS service is about $60 and FedEx is over $40.

I emailed the seller to tell him the actual cost is way higher than Ebay's estimate for the listing, and I don't expect he'll be happy about it.

I looked for a way to put in the actual dimensions and cost when I made the listing, but Ebay defaulted to USPS for $17.20.

I don't want to cancel the sale, and I'm concerned about taking a hit on my feedback already if I ask the buyer for the actual cost.

Could I have done something different to avoid this? Why did the listing default to such a low price for an item that's 60" long?