High stake exam resit and difficulty with focusing

Hi, i'm a student in computer science with really bad difficulty to concentrate (i suspect adhd but still havent been able to get a diagnosis).

This year i had a really important math class which i really stupidly never went to. I failed the exam and i have to go to a resit, where if i dont get at least 50% i fail my degree. I have 2 weeks full time to study but i feel like i'm going to lose my focus and i'm really stressed about not passing the exam.

I need tips for organizing my studying, managing my time and actually learn stuff while i study. What would you recommend?