By constantly training, you should be able to increase your cognitive score. Still, the rate of increase should slow down as the higher you are the more difficult it gets to increase your score.
Bear in mind that your cognitive score is a precise measure of your current cognitive state of a variety of cognitive skills. It is therefore hard to change dramatically your cognitive score from one day to the other as your own natural cognitive evolution takes time.
The cognitive score that will appear on your profile will always be your best score. In this way, you can complete as many training sessions as you want without being afraid facing a lower cognitive score on your profile page! After each training session, you see your cognitive evolution.