You are not including a specific shipping fee to the US. So for now what you can do is send your buyer an invoice with the shipping fee on it. When you make the invoice for him, add the shipping fee but do not click Recalculate. That never works. Just add the shipping fee, Preview, then Send. The following link will tell you all about invoices:
http://pages.ebay.ca/help/pay/checkout-invoices.html#sending