What about exams do you struggle with it?
Is it the content? Revise your material again, learn the theory, start with basic exercises to build confidence and then do some exam questions on areas of content you struggle with?
Not finishing on time? Try focusing on the question without a time pressure and doing the same question again with a time pressure. Check to see if your answers were correct, if so. Then try and write down your thoughts when under timed and non-timed conditions, what are the differences and then address those.
Too much pressure, anxiety, stress? If that happens, when you do the paper. Why does it happen?
If it occurs when you do a "tough" question=> Either do another question that you know you do well on to build confidence or close the paper, close your eyes and just breathe. Take a few moments to calm down and have thoughts that you can do this!, you studied all this year on this material, so they haven't asked something you haven't learnt! When your ready, then go back to the question and look at it again and do it step by step. It is better to get a question with no mistakes and miss a few, then do a plethora a question full of mistakes.
If you feel pressure beforehand and it doesn't dissappear or even worsen when doing a paper. You need to remind yourself, you are ready for this, you know what they can ask you. Since your doing practice exams, remember you can only improve and that with time you will.
"Honour the work and it will honour you".
I hope this helps, if it is something else that I haven't covered or if you want some more indepth then just shoot a reply here or PM me.
You aren't the only one going through this, many people struggle doing exams and many people have overcamed them as well. Don't see yourself as someone who won't.