Apple Mail is signed into email account but not showing mailbox.

Hello,

Recently, I tried to signed into a gmail account to see them in the mail app in my MacBook Air. I was part way through the process when and unexpected event caused me to quit out and close the app. When I tried again to sign into the account, the Mail app said that it was already signed into it. However, I don't see the account in the mail app, in the mailbox list, or the preferences. I'm stuck at this point, not seeing any option to solve it. Is there any suggestions to fix this issue?