Hi phatanita,
Firstly welcome to the forum.
Secondly, if you have modified the lot in any way from its original form, you have to save it to the library before you move out of it to go to another town. I do this frequently. Save your game first, then in Edit Town, save your Sim (Household only) to the Library, then evict your Sim from the house to the clipboard, then save the house into your Library. Now you have a copy of your Sim with current skills and inventory and a copy of the house to the library. You can move via the in-house mechanism or just go to your new town and add your Sim to any lot in the new town via Edit Town.
When you want to travel back to Bridgeport, open Bridgeport from Main Menu. In Edit Town, remove the standard house or lot where your saved house was and place your saved house from your library (the middle tab in Edit Town). Your house should be unchanged from when you left in the first place. Some items from your Sim's personal inventory may end up in the family inventory, but other than that, this is the simplest method I know of to preserving your modified house.