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You are in a boot loop because you tried to boot the phone without an OS successfully installed.
Hold both the power and volume down buttons at the same time until you return to the bootloader interface (fastboot menu).
Once you are back at the fastboot menu, you can flash release again using the web installer. If the flash fails don't press any buttons on your phone, but instead make a note of the error message, and come back here with the message to ask for support.