whoami is not who I am!

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.