Are you complete beginner in Linux world or you have somewhat experience?
The reason I'm asking is, there is another installer that needs a little bit more input from the user and it could be overwhelming for complete beginner. See link to the guide bellow.
I have one computer that several different Manjaro flavors installations all failed but when I tried manjaro-architect installer it worked. Your case is similar to mine (and few others) and one of solutions was, to boot from gparted live disk and set boot partition. But mine system is msdos no gpt like yours.
Anyway, try with this one (guide):
ISO for download: