I have just calculated 3 options (assuming you are doing the exact same units as the OP). To get an overall D*D*D*, you will need to get a Distinction for every unit and for three of the four exams (You can get a Merit for one of the exams). If you get a Distinction for every coursework unit and Merits for the four exams, you can get D*DD. If you get a Distinction for every coursework unit and passes for the four exams, DDM.
The exams are critical for the new BTECs and it is very rare for learners to get a Distinction for all four, so please bear this in mind. I don't have access to the results for Applied Science so can't give you a breakdown of how many learners did achieve a Distinction for previous years, but your teacher should be able to access this information for your own centre, so have a chat with them.