Determine the hydronium ion concentration in a solution that is 0.0028 M HNO3. Answer in units of M

Please explain procedure, my answer was 3.6 x 10^-12 and apparently it is wrong!!

Thanks

HNO3 is an oxyacid and also a strong acid, meaning it dissociates completely in water.

Because HNO3 has a very large Ka value, we can assume [H⁺] = M

so the hydronium ion concentration = .0028

if you want reassurance, check out this website: http://nitricacidsite.com/your-questions-about-ka-of-hno3.html