I really wish you much success and hope that you have understood everything correctly, because usually lives/people depend on a house construction with a loan.
Actually, the utility connections are not included and with gas somewhere around 10k€ and up.
Also construction electricity/construction water, construction site setup or construction access road are not included and are often, how should I say, “concealed.”
Are you sure that, for example, 40 power outlets for the entire house are enough for you? Do you possibly also need to upgrade the sanitary installations?
The general contractor cannot guarantee you the civil engineering work as long as there is no geotechnical report & soil analysis. What will you do with the excess soil? What happens if you find rubble in the ground? The general contractor will not remove that for free! The cubic meter of poor soil costs us only to dispose of around 55€. For a 150 sqm house with a concrete slab, that easily adds another 3k€ on top.
Where in your offer does it say “bauseits” everywhere?