How do I proceed when I can't kill the Wall of Flesh? [duplicate]

There's a few things you can do if beating the boss isn't an option:

• Get complete armor sets. If you have Necro Armor and the Molten Helmet, you can't really take advantage of the full armor set bonus. Find what "role" you play best as (either Ranged, Magic, Melee), and get the appropriate armor set for it. Since you seem to play as a ranged character, considering getting the full set of Necro Armor to give a higher chance to not consume ammo, especially for an expensive ammo consumer like your Star Cannon
• Prepare a skybridge in Hell. Makes the fight much easier to manage. You don't want to fall into lava just when you're about to kill the boss, so manage and prepare it carefully.
• Stock up on potions. Cannot emphasize this enough. Potions are a must have when fighting the boss
• Go exploring! Get some accessories for your character. Digging deep into the ground to hunt for Hermes Boots so you can build Rocket Boots and other accessories can make fighting tougher bosses much easier. You can also try going for the Ankh Shield, a combination of the Ankh Charm + Obisidan Shield, which provides extra defense and provides immunity against most debuffs, something especially helpful in some of the later tougher bossfights.

This link here also has some tips and general guidelines on how to fully prep up for a fight against the wall of flesh: