pH is much higher than pK2, and HSO4- will dissociate at this pH, hence H+ will be largely due to a dissociation of HSO4-
Difference between pH and pKa2
is not that large - pH = 3, pKa2
= 2. 1 unit difference is hardly "much higher".
Besides, problem doesn't state anything about the source of pH - it only states pH = 3.0. Thus assuming that HSO4-
dissociates further is equivalent to stating "although we are told that pH=3.0 we are going to ignore that and assume that pH is different". I can't see any reason for doing such thing.
As I read the question it states that pH was checked/measured at 3.0 - and we have to just calculate ratio of SO42-
. Note that if the solution has measured pH=3.0 this value already takes HSO4-
dissociation into account.
What you propose is a solution to a completely different question - what will be the change of pH in the solution that starts at pH = 3.0 when HSO4-
is added. But as concentration of HSO4-
is not known, such question can't be answered.