IS the map its self a prefab (before you exported it) ? If so you may have to separate the building assets from the map if they came as a package. If you built the map from scratch, you should be able to just drop and drag them into the hierarcy and compile them as a prefab with your map when your ready to export.

Thanks! There was supposed to be a ton of assets but I didn't know how to put them in game, but it looks fine like this ngl

finally a new map! looks great with a lot of variety!