Don't Worry About It is a rare Enchantment — Aura card from Mystery Booster 2 (MB2), collector number 592. Current market price: $0.22, TCGplayer market prices via Scryfall.
Enchant card in your hand (This Aura remains on the battlefield. If you play enchanted card or it otherwise leaves your hand, put this Aura into the graveyard.) Enchanted card costs {1} less to cast. When you cast enchanted card, copy it.