I think I solved this on my own. It's not elegant, but it seems to work.
For "rent paid for your entire home", you don't put the rent in for the entire year (and assume that TT will to the calculation for how many months you put in earlier).
Instead, I ignored how many months I put in and instead under 'rent' just put in the rent for those months of the year that I used the office.
It then calculates the percentage of the rent you put in, which should give the correct answer.
(TT should put in better instructions for this section addressing this!)
If you have a better solution, please share!
Thank you