> I can't seem to get it working. Seems like I haven't installed Python 3
> correctly
> Terminal comes with this prompt everytime: -bash: python3: command not found

Judging by the error message, yes, you're typing in the right command but it can't find Python 3. You could try replacing python3 with /usr/local/bin/python3 or /usr/bin/python3 and see if either of them work. Otherwise, I'd try installing Python 3 again, and make sure it includes the command line version. (I forget if it's a separate option, sorry.)