No. Depending on what the charge was, you may be able to vacate the conviction so that it does not appear on your criminal history as reported by the Washington State Patrol. Take a look at RCW 9.96.060.
I agree with Mr. Kertchen. It is too late to get the diversion back. But you may be able to vacate the conviction. That can take some time to get done, so you will want to contact an attorney to get started ASAP.
That is not at all likely. Most likely you will need to get it vacated. A lot of attorneys handle this type of thing. Your record since that incident will be key in determining if you can vacate or not. Sorry, but this is going to cost you a lot more than the original $250 you owed.