With B and C in the same car, you have what used to be known as a "bedroom suite". There is a partition between the two rooms which you can ask your attendant to open so that you can share the space. Luxurious, and you can ask to have it open during the day but closed at night for privacy if you prefer.
You should call Amtrak and speak to an agent and ask to see if you can have your reservation modified...that's the key word, "modify"...so that you can have a bedroom suite on your return trip as well. A good agent should be able to do this at no additional cost IF space is available. That's a big "IF". So if the agent says no space is available at this time, thank him/her and keep calling back, preferably at breakfast time every morning. Somebody may cancel.
Edit To Add: Just to make it clear, on Superliners (west of Chicago plus Capitol Limited), only bedrooms B & C or bedrooms D & E may be combined into a suite. Bedroom A cannot be booked as part of a suite due to the physical configuration of the car. On Viewliners (single level cars operated in the east), there are only two bedrooms A & B. These can be combined into a suite if you book both.
Edited by ehbowen, 29 June 2017 - 11:42 AM.