I can understand why you may be nervous, but according to Use the Find My app to locate a missing device or item, when you...
Mark as Lost
When you mark your device as lost, you remotely lock it with a passcode, keeping your information secure. This also disables Apple Pay on the missing device. And you can display a custom message with your contact information on the missing device.
What happens if you erase a device
When you erase your device, all of your information (including credit, debit, or prepaid cards for Apple Pay) is deleted from the device.