FNAME merge tag is displaying first and last name

FNAME merge tag is displaying first and last name

Hi! I am just building my first campaign. 

On my sign up I have used a simple form which only requests Email and first name. When it processes, my contact list is saving the first name to both the first and last name field. 

I have included the FNAME tag in my autoresponder, and set the campaign live. 

On testing, I have signed up my email address using my form, inputting only email and first name, and for some reason the email is duplicating the first name (or potentially displaying the first and the last name field?)

Any help gratefully received!!