EFI Partition not found, tried MountEFI multiple times but no luck.

Hi, I'm trying to install macOS Catalina on my build. I'm using OpenCore and finished my EFI folder already. One thing that I've been struggling with is that I cannot mount EFI partition to my USB. I tried using MountEFI the first time and the EFI Partition showed up. However I couldn't paste the EFI folder into the partition so I clicked eject it. Now, when I tried to use MountEFI to re-mount it but it doesn't work anymore. Please help me. I tried switching to another USB and other Mac but it doesn't work. Thanks for your help.