Technically, it does not say. So it is up to the DM. A few valid interpretations:
1. There is not enough room for the spell, so it does not manifest (the spell slot is not used because there was not a valid target).
2. The spell intersects the solid objects like walls and doors which are locked in place in the dome, but the dome extends beyond them.
3. The dome takes on an irregular shape as it conforms to its available space.
Which best fits your feeling of how it should work is the one you should choose.