Not able to recall during exam.

Practice what ever you study by writing in a rough note.  On a chart draw diagrams / formulas / important points and stick it on your room wall. Take up mock test in examination condition, probably it would help. 

Meditate for few minutes to calm your nerves and you will be able to recall all that you have studied. Wish you good luck.

In addition to Mr. Satish tips- revise at end of day what was studied that day- revise again at end on next day the previos day and at end of week revise the entire week studies. Students who do well in examination seem to be applying this.

Dont expect to remember more than 70% of your preparation during exam. But if you revise more times the % of remembering increases. Also it depends upon person to person. Some person recalls everything after 2 revision while some recalls 60-65% even after 3 times of revision. So analyse yourself well and find time to revise accordingly.