Different ppl produce different vol of milk. It's a demand n supply issue. Also, some people do intentionally boost their supply for storage through expressing after latching on.
Is this the 1st time you are pumping or have you always been pumping? If you've just started pumping, give it some time. Once your boobs get used to the pump, the vol of milk that is extracted can increase. Also, the amt of milk you get thru pumping is approx. 70% of what your baby extracts via latch on.
For me, my supply is lopsided. 1 side produce approx 1/3, the other side produce approx 2/3 of the total vol per session. Each session, I will get between 240ml - 300 ml when baby was 4 mths old. I dont't pump out after latching on.