Room numbers with an odd number and then an even number one more than the odd number are across from each other. In other words, roomettes 3 and 4, 5 and 6, 7 and 8, etc. are opposite.

Amtrak's pattern of booking roomettes is fairly strange...they do seem to alternate upper floor, lower floor, upper floor, lower floor, etc. However, you would think that, given availability, they would place two rooms on the same reservation adjacent or opposite.

It may not be too late to rearrange--call Amtrak and see. Apparently, moving rooms without changing fare buckets requires some magickery in the Amtrak computer system, and some agents aren't as familiar with how to perform such delicate maneuvers. If the agent wants to charge you more for a room swap, ask for the agent's supervisor or thank the agent and call back and speak to another agent. It's not unheard of to have to talk to four or five agents before you get the correct answer...