Get stuck when installing macOS

To all the kind folks who are always ready to help:

I found myself stuck in the process of installing a new version of macOS onto my MacBook Pro 2012. Please help 🙏🏻🙏🏻

To cut the story short (please bear with this poor desperate soul):

1. I smoothly followed all the steps of this YouTube video https://youtu.be/_PiGyhudHeA?feature=shared (except that I’ve chose “Reinstall macOS Sequoia” over the existing one without erase the drive first) and reached the last phase stage of the installation - I could boot my Mac using the USB drive, and yet haven’t install OpenCore into the internal hard drive.
2. But then I decided to redo the process again, thinking it would be better to erase the disk first as the video recommended.
3. I erased the SAME (I know…sigh…) USB, and repeat the installation process from the very beginning.
4. Everything went well - the macOS Sequoia installer was successful created - until I accidentally press “No” to the question “would you like to continue and install OpenCore to this disk?” and restarted the Mac without pressing the Option key.
5. I now found myself stuck. The option “EFI Boot” was there even I reboot the Mac and press the Option key. The two options “Macintosh HD” and “Install macOS Sequoia” did not lead to anywhere. I now realised how stupid I was.
6. Please help.