Username issue

Hi,
Hope one of the mods can help. My 'username' is IamShell but I noticed today that I was logged in under 'name' with my full name showing (even though IamShell still appears as my 'username' in my profile!). I had to go to my profile and change my 'name' to just my initials and now I am logged in as 'username' MS.
I expect for the site's purposes my 'name' has to appear in full in my profile but, as I said, I can't do this as it's showing as my 'username'/ 'logged-in' name. How can I get my 'username 'back to IamShell so I can supply my full name under 'name' in my profile? I get a red circle with a line through it when I hover over my 'username' in the profile editing area
Hope someone can help... Not idea why this has happened Thanks.

Thanks, Gordon...
I feel stupid but under edit profile information, my username has always been IamShell and I'm sure that my name (directly under that) has always been my full name. I did log in successfully with IamShell but, as I said, I appeared on the forum as my full name and so had to edit to my initials, making me now appear as MS on there.
I have no idea why I suddenly stopped appearing as IamShell in the forum as I'm sure I've not edited any names in my profile... I've always logged in as IamShell and had that name against any of my posts/ replies too...
I want to both log in as IamShell and appear as IamShell on the forum. Is the answer to
put IamShell under 'Name' too? That way will I both log into the forum and appear on the forum as that name?
Sorry if I am making this more confusing than it is!

Thanks, Gordon. I think somewhere along the line I must have inadvertently changed my name from IamShell to my full name, allowing my full name to appear on the forum. Whenever I log in I log in with user name IamShell and then enter my password, and then I also appear as IamShell in the forum (usually!). So,I think I need to change both username and name fields to IamShell so I appear as that on the forum. I hope that's right. Thanks, Gordon.