Creating a new shower area. How to fill void and studwork.

[mrbg07546]

Hi. I have removed our old "boiler room" and extended our bathroom into it. The part which used to be the room is now our shower.

We have cement boarded the shower area and I have a few questions.

1) there is a small area where the cement board does cover? How do I fill this gap.

2) the studwork which is next to the old frame is slightly ahead of where I put the cement board. What could I do here

 

[Cgas]

Tape & seal all the joins first, corners too.
Can't really make sense of the second picture. Cement board finishes into a corner what's the white just a painted wall? Use anything to fill if it's being covered? Can't see if it's going to be in shower area or not.

On the third picture you should of packed the studwork out so you could board right upto the door frame. is the timber going to be within the shower enclosure or not ? Where's the pivot door going?! If it's outside of shower the options are easier. Could just tile over the timber if it's flush but not ideal.