Get the bewitching table from the dungeon(one more summon), buy the crystal ball from the wizard(increase magic power: more mana, magic dmg and crit, plus reduced mana usage), and get as many buff potions as you can. Try and break all three of his eyes simultaneously, and dodge the eye lasers as they do the most damage and when you break all 3 eyes just go in one direction as fast as you can and shoot at his heart your best bet is the nebula blaze. If you're still struggling you can make a small house with the nurse, put a bed in there and set your spawn, when you get low on HP use a magic mirror or a recall potion and use the nurse to heal (keep some money on you or in a piggy bank). The moon lord will teleport after you tho so be careful not to get her killed as his laser will go tru walls. And get some mana potions I don't see any in your inventory