very minor help with pre employment checks

Employment history for pre employment checks asks whether I've been employed within the last three years, which I have. However, I've only been employed for about 2 and half of the last three years and when I try disclosing this it doesn't allow me to and asks me to enter a minimum of three years and doesn't allow me to carry on with the rest of the checks. As embarrassing and as stupid as it sounds, I'm a little stuck here. I don't want to fill it out incorrectly as I'm really excited about the opportunity and don't want to mess up. Should I just respond with "No" following the question "Have you been employed within the last 3 years?" or should I be doing something else? I understand this may be the dumbest question ever asked on this sub but any help would be greatly appreciated. Thank you.