Adverse Possesion & Boundary Dispute

[George Kamerzan]

I purchased a house with .33 acres in WA state, after carefully measuring it seems I only have .27. Apparently the neighbor to the back and side of me has been using my land(he built a little road for his truck and built a shed. My property should continue into his yard for about 20 feet and run about 115 feet. What should I do, I owned the property for a year now, I believe I have title insurance. Thanks!