The switch to ECQB2020 just seems a bit premature, considering there is hardly any study material available as of today. Quite a few other member states postponed it untill xx/xx/2021.
However, the UKCAA isn't the easiest to do you written's under, considering they're constantly updating their questions and making it harder by type-in questions, 'select multiple correct answers' questions etc... So it doesn't suprise me in that sense.
Just keep a sharp lookout on the Facebook groups and hope that some other students did their exams under ECQB2020 just before you.
Your ATO should provide adequate training. They've probably been briefed by the UKCAA and should point out the difference between your books and the new LO's etc.
Goodluck!