Be sure to incorporate timed practice sessions into your preparation. Without the constraint of time, it's sometimes easy to be deluded about what you know and can do.
Adding the time constraint means you will have to work faster to complete questions and this becomes problematic if you don't know your stuff!
When time is up in an exam - you must stop work. Practising as if you are in the real exam allows you to try out your time management strategies too so that you can ensure you respond to all questions and leave no marks behind by simply omitting questions.
Set yourself a timer and act as if it is the real exam - if you are working at home let your people know you will be busy for the next 2hrs (1.5hrs) so that they don't disturb you.
Use one of these ambient exam sounds audio files to get you in the zone!