How do I expand the surface area of the inside of a wall that I generate using data

I am currently building a wall using the cesium plug in this wall is generated with geo-data that gets converted to unreal engine positions using cesium. This data was collected by a car driving around a part of Amsterdam. The route that the car rode looks roughly like a letter T. I am trying to expand the surface area in the middle of this T

How are you generating the rectangles in the first place? Is this a feature of the Cesium plugin?

I just loop over the array transform the longitude and latitude to a vector in Unreal then I rotate it based on the next value of the array and then I just add a static mesh component