Right of way taken good?

The following situation: I'm standing at the entrance to a roundabout. Behind me, I see an ambulance approaching with its blue lights and siren blaring. Another vehicle, which normally has the right of way, was approaching the roundabout. Since the entrance to the roundabout is too narrow for two vehicles, I entered in front of the vehicle already entering the roundabout. This allowed the ambulance to overtake me in the roundabout.

Did I act correctly or was it too careless to take the right of way of the other vehicle without thinking about it too much?

Just for your information, I've only had my driver's license for a week and am therefore still relatively shaky on the road.