I think you just bought the Nexus 6. In this case, I would exchange the device at digitec, as there may be problems with the exchange after failed flash attempts.
I also bought an N6 (64GB white) last Friday and first wanted to update it to 5.1 with the result that the N6 was stuck in an endless bootloop. So I immediately went to digitec and the device was exchanged without any problems. Back home, I tried to update again with the same result. Bootloop. So I went to digitec again, but this time I got an N6P. The thing now works perfectly despite the small November update.
I would therefore strongly recommend an exchange if the device is still new. You might have more luck with an exchange device.