Floor plan design of a brick house with approximately 145 sqm

However, it is not possible to build a larger semi-detached house or something similar.

In front of my daughter's school, a semi-detached house has been built on 400-500m² (I don't know the exact size). One half has now had the outdoor area landscaped. There is a parking space, the path around the house lined with a few individual flower beds, at the back the terrace (by the way, facing north). That's it, the residents can probably do without purchasing a lawn mower. Because there's no lawn...
The area is simply very small, and it's similar for you. There's no helping it, you'll just have to deal with it now.

The price per square meter is €499/sqm. However, it is not possible to build a larger semi-detached house or something similar. The demand for the middle house was apparently not very high - no new neighbor has introduced themselves in over two weeks. The high demand in the NBG was more for the corner houses or the semi-detached halves, less for the middle terraced house.

"Not possible" is often relative. If no one wants the middle, you can still politely follow up with the building authority, in case you actually agree with the far right and they loosen the money. An intensive conversation about the difficulties of a subsequent "third" in the middle, and a joint appearance of the parties, might soften the officials. Everything in life is negotiable, especially in construction.