If it was shipped FLAT RATE; good news is that has $50.00 insurance on the package all ready without your having to pay for Insurance.
https://www.usps.com/ship/priority-mail.htm
Features
Free Package Pickup3 service at your home or office
Includes USPS Tracking® when you ship online and at retail4
Delivery in 1 to 3 business days.
Includes up to $50 of insurance5 with most shipments6 (restrictions apply)
No surcharges for fuel or residential, rural, and regular Saturday7 delivery
Flat Rate, regional, and prepaid pricing (retail only) available