Brown spots on my little seedlings

Does look to be a bit of burn. Odd pattern from what I'm used to seeing but its likely the cause. Don't wet the leaves when you water either if any get wet dry em off asap. the lights will burn wet leaves like magnifying glasses. Overwatering does not cause this type of damage. Its normally just droopy leaves, long term overwatering can lead to root issues like rot and overgrowth of nasty organisms in the soil. Best to start a diary and track your grow so other have a better understanding of it should you need to ask any more questions with it.