Hi again. The pot really looks big enough to me, but potting soil is notorious for drying out and then it's troublesome to get it wet again, because of the peat content in it. If you turn the pot on its side and slide the plant part way out of the pot, you should be able to see if the potting soil is uniformly moist. If it is dried out, just setting the pot in a large tub or something, and letting it soak for a few hours should help to re-hydrate the potting mix. A little plastic kiddie pool would be perfect if you don't have something else big enough.
Your fertilizer should be great, although 25lb. sounds like too much even for a big tree in the ground. Did you mean 2.5lb. maybe? Even that is a lot for a little tree in a pot.
The spots on the fruit are very likely just cosmetic, a little bit of rusty fungus or mite damage when the fruit was small would leave a lesion like that on the peel. Commercial growers generally spray for fungus and mites regularly, so that's why fruit you buy looks so perfect. It's pretty rare for home-grown citrus fruit to be perfect.
Um, hate to say it but it would be a good idea for you to pick off the remaining fruit right away. This will help your tree to recover, because it's putting a lot of energy into fruit right now, instead of growing leaves and roots like it should be.
