A couple of things. It does not sound like you are booting from the USB. It is important to use a 16 or 32 GB USB stick (not a USB drive) formatted FAT32 FULL in another Windows machine. Here are my standard instructions:
Go to https://support.microsoft.com/en-us/surfacerecoveryimage
(with a different Windows computer if yours is not working properly)
and download a recovery image for your Surface. You will need a 16GB or 32GB USB stick (also called a flash drive) formatted FAT32 (use a Windows computer). You can't use an actual external USB hard drive for this and don't use anything larger than a 32 GB USB stick*. Best to purchase and use a new, previously unused USB stick for this. Use FULL format and not quick format and give the volume a name like surfboot. Unzip/extract the recovery zip to the root of the formatted USB stick.*
There are full instructions and a video at https://support.microsoft.com/en-us/help/4023512/surface-creating-and-using-a-usb-recovery-drive#download
To insure you boot to the USB, you can go into the UEFI and change the boot order by dragging USB to the top of the list:
- Shut down your Surface.
- Press and hold the volume-up button on your Surface and at the same time, press and release the power button.
- When you see the Surface logo, release the volume-up button.
The UEFI menu will display within a few seconds.