Bricked my Nubia Z9 Mini - Please Help

Dear XDA--Developers Team,

I just bought an Nubia Z9 Mini and wanted to install a custom rom with the google play store preinstalled. In the process I bricked my phone. I am really desperate here and I hope someone can help me.

What I did:

I am new to all of this, so I followed this tutorial:
https://www.youtube.com/watch?v=ix7rrKS4keI

and tried to install this rom:
http://www.needrom.com/download/nubia-z9-mini-rom/

Furthermore I used this to install TWRP...

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