Get on google street view. There are a lot more than three wide open entrances in the wall.
Entrances or gaps? An entrance can be opened and closed.
Either way, the Vatican City can, and often does, restrict access even through the “wide open” gaps in the wall. That’s the nice part of being a walled city, you have a relatively few access points that you need to control. No fortress is free of any access points, since that would make it useless.