There is a ton of missing detail.
1. What is your final destination?
2. Is your final destination on AS?
3. Is PDX-Final Destination to be booked on the same ticket as EUG-PDX?
Depending on the answers to these questions, there are different approaches which don't require going through the rigamarole of EF and then finding out that someone else has snagged the seats while you are online and waiting to hit Send.