Actual shipping cost twice as much as buyer paid

[webehd]

I am an experienced ebay seller.  I just sold a heavy 12 pound dartboard. I opted for calculated shipping, and entered the exact dimensions and weight of the box.  When I received the paypal payment I was surprised to see that the buyer had only paid $17.50 to go halfway across the country. When I went to print the label, the actual cost to ship was 36.50---the same cost for Priority or Parcel Select. I have never had this happen before, is there any way to be reimbersed?