Wow, it's like that time I saw someone else end an email with "Retards" instead of "Regards". While I've never done it, I admit I've sometimes thought about it, even prior to that case :)
More seriously though, as @GrayCygnus commented:
and N are wayy to close each other on Qwerty keyboards
which is true and also applies to letters g and t in my coworker's slip above.
I can say it was so obvious to me that it had been a typo, that I never even mentioned anything and never observed anyone even talking about it. (People around me were reasonable.) In fact, I'm not sure he's aware of his typo to this day :)
That said, just send a simple email apologizing and noting that it was typo should be enough for reasonable people. Keep it short and simple.
What approach could I take to apologize for my typo?
My suggestion is:
Hi all,
I just realized I made an unfortunate typo in my
previous email and wanted to apologize.
I meant to say that <insert whatever here>
was **B**igger.
Best Regards,
<your name>
Make sure you send it to the exact same audience.
In addition, one member of the audience is African - American.
I'd suggest not assuming that just because someone is black, they must also be "African" too. There's a lot of black people having nothing to do with Africa in a bunch of other places in and outside of the US. If they're US Citizens, they're just Americans. That's it. :)
Did I damage my professional image at my company?
I don't think so, if we can assume everyone is reasonable. Much less so if you send a simple apology noting that it was an unintended typo. Do not grow your simple typo into an incident of epic proportions.