Hello Ella Shay!
I dunno what photo editing software you have but this is what I got from the avatar upload page:
"Note: The maximum size of your custom image is 110 by 110 pixels or 78.1 KB (whichever is smaller)."
So you need to squish your picture down to the above specs. Maybe even smaller... but try the above ones first. I had to adjust mine a couple times before it was officially "blessed" and put through hehehe!
Welcome to the boards! Are you an Atkins plan person as well? (I'm doing low-carb WW at this point but have done 100% Atkins in the past.)