hmmm I made a small tutorial to change it in your emails that you are sending out. You would have to check in your address book to see if you have yourself there and if you included a middle name. If it is happening due to the way you set up your account, this may work:
Follow the images here to get to the place where you set your name. First click the settings wheel in the top right hand corner and select "more mail settings" from the drop down box.
You can click on the images to enlarge them if you need to.
Is it possible that you put Christopher Nicholas on the first line for your first name? If so, remove the middle name there and it should go away if this is the cause for it showing up.