If you overwatered last week, I wouldn't water again yet. The size bag you are in for that size plant will keep it going for a while.
Nute burn usually happens at the tip of the leaves, so it's not that.
It can happen is you accidentally spill some feed on the leaf and as the water in the feed evaporates, it becomes very concentrated and can burn your plant.
Sunburn is definitely a thing. If you have water drops on your leaves when the sun is out they act like mini magnifying glasses and burn little spots.
What you have is definitely not from the sun, because that is quite difficult to achieve when the plant is inside and not in the sun :P
My guess is you spilled feed, but that is nothing to worry about. Other than that your plant is looking very healthy, so let the soil dry for a while and she will perk up again.