Can't boot without the USB installer (Open Core 0.6)

This is my first time setting up a Hackintosh and I used my old laptop (HP 450) for it.

I followed the original Dortania guide and I successfully installed it but I can't seem to run it without plugging in the USB stick that contains the installer.

It basically shows me that:

Legacy Mode enabled -> Can't find boot device

Legacy Mode disabled -> Boot device not found. Please install an OS on your hard disk.

I've already done this post-install guide where I'll mount the HDD's EFI using CorpNewt's MountEfi then copying all the contents of the USB stick's EFI folder into it.

I already tried running the BootInstall.command on the partition that contains the HDD's EFI but it fails saying that I can't write on a read-only directory.

I made the installer on a Windows machine and the guide has this note that I can't quite understand:

Note: Installers made with gibMacOS's MakeInstall.bat on Windows will default to a Master Boot Record(MBR) partition map, this means there is no dedicated EFI partition instead being the BOOT partition that mounts by default in macOs.

Any suggestions on how can I fix this problem?