GCP compute engine permission denied (public key) after manual edit authrized_keys

Question

PROBLEM: I edited ~/.ssh/authorized_keys manually using vi to add my mac's public key. I exit from ssh shell and try to connect via vs code remote development. Then, I can no longer access my VM instance. (ssh, ssh on console or else. in every way) I assume my authorized_keys is damaged.

What can I try more?

Thanks.

WHAT I HAVE TRIED:

1. edit metadata in gcp console to add my ssh key. (old one and new one with username)
2. resize disk space 10 -> 15 -> 50