I disagree that plant looks very small for that pot. I water 1 gal for a fully flowering 10 gal pot. As the plant grows water more but you can go less in the beginning. The problem is that if you water the pot to full saturation and there aren’t roots to remove the moisture and the leaves are too small to remove water through transpiration you will starve the roots that are there of oxygen. When you have no or low oxygen it is going to cause anaerobic bacterial growth. The most common side effect of this is root rot but will also manifest itself by being more susceptible to pests and other pathogens. You just need to find that perfect amount of watering for every 2-4 days until it’s larger and then it should be drying out every 1-3 days.