Can't add my second Gmail account to Mac Mail

Here's what I did:

I went to System Settings > Internet Accounts.

I chose Add Account and chose Gmail. I typed in my 2nd gmail account email address and password. Then I verified it on my browser (gmail.com).

All that did was list the account in System Settings > Internet Accounts.

When I open Mail on my Mac, it still only shows me my originia Gmail account. I've tried quitting and reopening Mail. And restarting my Mac. To summarize, I'd like to be able to access both of my Gmail email accounts on the Mail app on my Mac. Thanks for any advice anyone might have.