Pirate Ship currently offers 4x6" and 2x7" label sizes. To select which format you'd like to use, head to your Settings > General Settings:
Keep in mind that you must set your label size before you create any labels. The size you select will apply to all label purchases going forward, and you will always need to head back to your Settings to make any changes!
Unfortunately, the size of a label can't be changed after it's been purchased. You would need to request a refund for the incorrectly sized label, change the Label Size in the Settings, and start fresh on a new label (Pro Tip: Use the Duplicate Shipment button at the bottom of the shipment page for the label you're refunding, so you don't have to type everything in again 😉)