This is arguably a clerical error, so you may be able to get this fixed on motion under CR 60(a). If not, you will have to move to vacate and enter a new order under 60(b). As you can no doubt prove the date of your marriage and the date you began to accrue your pension, you have a good argument that the outcome is the result of clerical error and does not reflect the original intention of the parties. However, this must be done within one year of the date the court signed the order.
No one can ever say for sure what the court will say, but I would say you have a reasonable chance of prevailing and considering the amount likely at stake, it is certainly worth trying.
Contact a WA attorney ASAP. You do not indicate how long ago your divorce was entered, nor do you provide the precise language of the pertinent QDRO paragraph(s) contained in your judgment, and this makes it difficult for a WA attorney to advise you without a one-on-one office consultation.
You may have a better chance of modifying or amending the QDRO than you think. Look for language in your judgment by which the court reserves jurisdiction of post-judgment QDRO compliance revisions.