Yea muun wallet is a terrible lightning wallet because it always need an onchain transaction because it pays lightning via swaps. On chain fees are high at the moment, that is why there is such a high fee. I would recommend getting a real lightning wallet like Zeus Mutiny or Blixt. This way when you pay 300sats on lightning your fee is only 0-5 sats depending on who you open a lightning channel with. If you need help setting up a lightning wallet feel free to DM me.