I never measure the amount of water I give ... truly... and I don't set up a watering "schedule" like "Monday I'll water, Thursday I'll feed" ... I let the plant tell me when it needs something and I let the plant tell me how much it needs giving it more water when the soil dries out... but I do hope you're not giving this little one a gallon of water!
At this point in the plant's life, you don't need to have any runoff - plus you want to water around the seedling and not right up next to it - you also want to make sure the soil dries out between waterings. The danger at this point is overwatering which is the state of being constantly wet (not how much you give at any one time). If you give it the whole gallon of water, it's going to take forever to dry out and it won't be the roots drinking it that dries it out and the roots really WILL be constantly wet... not good.
I know it may not seem as if you're giving her enough water since she's in a 5-gallon pot and there's a LOT of soil there... but it's a little plant with very little roots. If I had to guess at the AMOUNT of water to give her now, I'd say 1-2 cups (and let it dry out).
Good luck..