Gsr is right. You need to figure out where you did wrong and where is your weak area. Of course you won't know for the real test. But you should definitely analyze your practise tests. Find the areas you are not familiar, the areas you totally don't understand, and the area you understand perfectly but often make silly mistakes. Consider your timing and your preference, find the areas you think you can make the greatest improvement and work on those. Think of it this way, if your real score is going to be 100 points lower than the practise test scores, and if you want 550 for the real test, then shoot for 650 for your practise tests. You are now getting 550 for your practise tests. There're lots of room for you to improve. From 700 to 750 is hard to do, but from 550 to 650 is definitely achievable. You can just go by the feeling and hope the best luck happens to you. You need to use your analytical mind. To really understand what you are doing. Then if by any luck the best luck does happen to you, you may even get better scores then you are prepared for. Isn't it great?
Keep on asking, and it will be given you;
keep on seeking, and you will find;
keep on knocking, and it will be opened to you.