JFDIY

You'd expect it to be able to heat the space to 22c especially as it's not even freezing outside, but it depends on what the original design was based upon, was it bedrooms? These have a lower temperature expectation and the pipe spacing might be wider on that basis. I'd consider raising the temperature to even 45c but depends on the construction and finish covering. Is the space you're heating confined, i.e. you haven't taken a dividing wall out and in reality trying to heat 70m2 with only 35m2 of pipes. Measuring the supply and return temp of each loop will a the clue to what is going on, might find all the heat is being absorbed by the screed and the flow needs increasing.

Clamp a length of 2x4 vertically to the joist, you should be able to twist them back to plumb using it as a lever.

Is there any means of positive pressure getting out, i.e is there an open stack on the system anywhere? Could be when another user on the system flushes it pushes a slug of foul air through one of your traps, you might just have the smallest trap depth in that room.