I thought I was the only "grown up" who can't sleep the night before Disneyland! My husband and kids laugh at me every time. I get so excited the whole day before as well. It feels like I'm on cloud nine!
Call the Costco you purchased the tickets from & ask to speak to the warehouse manager. They should take care of you especially since you have the info from Disney. The tickets sold at Costco came directly from Disney, not another source. Costco will take care of you - I've worked for them for over 25 years & at our building we take care our members.