The reason you should ask your own attorney is manifold. But the most obvious is because what you say does not make sense. If the case was dismissed, you do not lose your gun rights such that you need them restored. Perhaps your case was deferred? Or perhaps you case was just closed. Either of those might trigger the 3 year waiting period. However, there are some arguments to be made as to whether you should have to wait on a deferred dismissal.
At your service,
If you already have an attorney, you should be asking him/her this question.
The information is for general information purposes only. Nothing stated above should be taken as legal advice for any individual case or situation.
If the charge in question was dismissed after a pre-trial continuance period of 2 years (typically referred to as a diversion, SOC or dispositional continuance) then you have never been convicted of the crime in question and should not have lost your right to possess a firearm. You may, however, have been ordered by the court not to possess a firearm during the period of continuance. Once the case was dismissed, this restriction would have ended as well.
If, however, you were actually convicted of the charge in question and only received a dismissal after completion of a deferred sentence, then you must wait three year before petitioning a court to have your right to possess a firearm restored. See RCW 9.41.040(4)(b): http://apps.leg.wa.gov/rcw/default.aspx?cite=9.41.040.