I don't understand, how do I get the number of damage dice to scale on the character sheet?

 You make an "at higher levels" modifier for 5, 11, and 17.

But my current ''at higher levels'' modifier has no effect on the spell's damage dice

Did you put the new damage dice value for that level? I recommend doing what I did to check this, and making a copy of fire bolt or something. 

Ohh... Thanks, after copying fire bolt I realized the problem, the scale effect type for this is Additional Points, not Additional Count

Hi, i was having the same problem and is now solved, but I would like to know what does the scale effect type Additional Count does.

i believe it fires more projectiles, like scorching ray or eldritch blast