I personally don't think that it is too big, but the use of the area makes it feel empty, in additon to the sight lines.
If you want to make a linear map, like you did here, I recommend you study the architecture of koth_viaduct. In order to make the map interesting, the map has a slight curve of places where the cannot be OP sightlines. There is also great height variation through displacements, which I think you should incorporate here. My map koth_grange incorporates this to an extent. These sort of maps usually have a long rectangular shape.
If you want to make a compact DM-style map, like koth_harvest, the map has the "loop around itself." By that I mean think of it like an arena map, which was koth_harvest's original gamemode. In order to protect spawn and add to the map, there is an obstacle in the way in order to structure the map. Ex. The barn building right in front of spawn on koth_harvest. These sort of maps usually have a square shape.
I highly recommend you redesign your map in future versions with these map structures in mind. If you want to look at decompiled versions of these maps click
here.
Impressive for a first map, this has potential.