Uniformly charged disk charge

fal01

A uniformly charged disk has a radius of 2.6 cm and carries a total charge of 3.6*10^-6C.

Find the electric field on the x-axis at a distance of 3.3mm away/

I really don't understand what I put for sigma.


this is what I have so far:

(sigma/2(8.85*10^.12))(1-( 1/ sqrt( ( .026m^2/0.0033^2)-1))


Sigma is the total charge/the area...

so sigma= (3.6*10^-6)/(2pi(.026)^2)=8.48*10^-4

I feel like I have some part of this wrong.