As a residential design/builder, I can understand how you might feel you need all that space, or how 900 sq. ft. might feel small. But you will get used to it.
For advice on how to live with less room, a few observations. You mentioned needing to fit into 2 11'x11' spaces. For comparison, my wife and I
share a 6' x 6' walk-in closet. And you can see the floor. The trick is to have less clothes. We each only have about 4' of hanging clothes, the rest is drawers. Use your basement for out-of season clothes storage.
For other areas, de-clutter. If you haven't finished unpacking, only un-pack what you need, not the things you usually have out. After a while, you can get rid of what you don't unpack. Check out these guys' story:
http://www.theminimalists.com/21days/Failing that, combine space uses. For instance, the laundry room might also be the rear door entry/mudroom and pantry, or include a bathroom. My main floor bathroom is 6'x12' and serves as the main bathroom of the house with shower, and laundry (stacked) and is accessibly designed, meaning you can turn a wheelchair in there.
Your office can be a corner of the living room. The dining area can double as a work space for the kitchen. An open plan like you have helps with this combined use strategy.
Looking at your floorplan, maybe you can move the laundry into the bathroom, and use the former laundry as your office, that sort of thing.
Good luck and congratulations.
Added after more thinking:
I would suggest looking at your furniture, couches and chairs up on legs and with open frames appear to take up less space than floor-hugging, solid pillowy ones. Also, arrange furniture so that you can see the edges of the room, where the walls meet the floor, this give the illusion of more space.