Session CBE difficulty

I have uk tx exam in march 2020 , my practice is all good except few issue :
1. My typing speed is good but somehow i get very confused solving questions in spreadsheet of excel in my PC using ms office ,I take too long reading information from question and putting it on spreadsheet but somehow i am twice as fast when doing written practice .So far I have just practiced using written technique .

2. I attempted specimen tax paper on acca website , i left a question incomplete and clicked next but when i went back somehow i couldn’t edit the cells , i can’t seem to find a way how to edit locked cells , it keeps on saying that cells are locked.

Any tips would be appreciated as i don’t wan’t to fail this attempt with poor time management . Thankx