Do not worry too much, too stress over supply issue is not good, stress affect milksupply
After baby is born, just latch on to feed, the more you latch, the faster the supply will build out. But of course, there is minority who really have supply issue, but give whatever you have for baby :-)
During confinement, drink alot of water and have a balanced diet, sufficient rest. Nowadays, got so many options of supplements like the nursing tea, fenugreek etc. You can consider to buy and consume after birth.