ha seangheng i think ur problem it's similar me too cuz when i have an exam in reading i'm not pay attention to read, but always think about another stories........ I think if wanna be a good reader it will be a bit difficult, but hope u will try by your own try to pay attention and tell yourselt that now it's time for you to have reading exam not to think about other stories and when you do your exam don't be nervous just do as much as you can

Anyway, it just my thought, but hope it will help you