Ive started Expressing milk for DD. I have bee...

Ive started Expressing milk for DD. I have been doing this in the morning as this is when i have most, DD sleeps all night. So far i am feeding from one breast, expressing from the other in the mornings. I generally stop at 120ml max as im scared i will run out of milk. Can you express all your milk?? im hoping to try express more so i can start getting ahead and freezing some. Does anyone have any advice??