whoami is not who I am! I login into my own computer as username geoff. When I open a terminal I have as prompt:

Geoffs-MacBook-Air:~ org1$


The org1 is my work username! I have no login of that username for this computer except for when I need a to access work from home, and I do this with VPN. At the moment the VPN is not connected. When I do whoami I get org1. I also did login geoff gave my pword and then did a whoami and still I get org1!

What is my computer doing? What do I need to do to have a normal prompt?

The real problem comes later, when I need (I believe I need) to use sudo and it eventually says that org1 is not in the sudoers list. I don't care for org1 I want me.

@Patrix EDIT

Geoffs-MacBook:~ org1$ id -a
uid=501(org1) gid=20(staff) groups=20(staff),61(localaccounts),12(everyone),402(com.apple.sharepoint.group.1)

Geoffs-MacBook:~ org1$ who am i
org1     ttys000  Dec 27 17:17 


Geoffs-MacBook:~ org1$ w
w: /dev/ttys001: No such file or directory
w: /dev/ttys002: No such file or directory
w: /dev/ttys003: No such file or directory
17:18  up 29 mins, 2 users, load averages: 0.52 0.29 0.17
USER     TTY      FROM              LOGIN@  IDLE WHAT
org1     console  -                16:49      28 -
org1     s000     -                17:17       - w


The org1 username is for work, which I can use remotely through a browser or VPN. There is no user on my computer with that name.
It seems that the short name and the username on your Mac do not match. To test this just type id and echo ~ to confirm that the Mac is fine, but the short name and home folder are not to your liking. Apple has an official procedure to fix this at http://support.apple.com/kb/HT1428 and we have several questions here that also cover the topic when people have found that HT1428 didn't work for them.

There are several procedures to edit the short name but they're all a pain. Furthermore, they often don't clean everything up correctly and traces of the old name you didn't like will remain on the system in folders and lists. Your best bet is to go into the users preference and create a new admin user with a password that you know. 

Then you can follow the steps on this other answer here to delete and re-create your account with all of your files intact and the correct short name  that you prefer. You will find that you prompt now matches the short name that you like. Before starting this process, you might make a good backup if your system just in case you make a mistake of my instructions are not clear or if the computer just crashes at the wrong time.