Room Type Change

I’m trying to change the room on the left (with the whiteboard) and the passageways towards the room into a public room for my sim’s already registered business but everytime I select public the room colour doesn’t change. 

I assume maybe it’s just a UI visual problem but the small business tab says that the business isn’t assigned, Therefore,  even though the room says it’s public, the game isn’t acknowledging it as so. 

The lot is set to residential. I’ve removed railings, staircases, friezes and made sure all rooms were considered closed rooms but none of these methods worked.  

please help!

When you say the small business tab says it isn’t assigned - do you mean there’s no lot set? Can you set rooms to public if you first assign the business to your home lot, which should make it a residential (small business) lot type?