Datavalidation error pops up too soon

Dear sir/madam,

I got a problem with the optipm named ''datavalidation'' and I would pleasured to know the answord for it. I want to get a maximum of two (possible) answers for a survey. The way I wanted to get the possible answers were as follow: 

I used the formule =COUNTBLANK('':'') with a selected range for the answers (see image). 

As next I used the option ''data validation'' and put a formul in the custom mode of this option with the condition, if L2 = 3 (the blank cells formule), their has to be an error in the screen (see image).

But the error pops up way too soon. It already pops up within the first answer given instead of the 3th (see image).

I can not see what I am doing wrong and I really hope that any of you can help me with this problem. If you got another way to get the same answers I also would like to hear from you! 

I hope hearing from you soon. 

Kind regards,

Mike van Es