I read on internet, the ws2812b use 50-60 mA when they are at maximum. I use that to calculate the battery I need. And I found 18 A
I think I made a mistake somewhere.
Yes you made a mistake
500 * 0.06 = 30 Amps.
Using 500 LEDs inside something some one is going to put their head into is way too much.
Using those strips is the right thing to do but you have way too many.