I would've asked for another room. There are no guarantees, but more often than not most hotels - especially those of Marriott quality - will try to accommodate their guests if space is available.

As to the thin walls - I would avoid this hotel in the future. Interestingly, I once stayed at the Hyatt out at Logan and was amazed at how poorly constructed the hotel was, particularly with regard to walls. There was a family of five Chinese people in the room next to mine and from the tone and tenor of the noise emanating from there, you would think that none of them got along!

Many people have disparaged sites like tripadvisor here, but with regard to thin walls I find their reviews quite helpful. At a good well built hotel (often the older ones) you shouldn't be able to hear normal conversation or TV at a normal volume from the room next door.