Seriously????
Just FYI for you.
A flat rate USPS Priority envelope to Canada is under $12.
A medium flat rate box is $27.
Depending on how much it weighs, it could be anywhere in between if send in a non-flat rate envelope.
And I've sent things to Canada via UPS.com that were sometimes cheaper than USPS.
You can easily go online to the website and get an estimate.
It would be nice if they picked up the tab but, ultimately, it's your error.
I don't know the value of the fabric you bought so you have to decide if it's worth it.
If it is, just tell them to charge it your credit card.
Or you can arrange the pickup online yourself.
They won't even have to label the package.
The driver comes with the label.