I agree, ditch it. You cannot take the risk that any type of bacteria have entered the bag. There is no way to keep the needle air tight. Also, if anything got on it when it was put on, the bacteria could have multiplied and worked its way up the line.
I know individual bags and lines are expensive from the vet, but you can buy fluids by the case from Costco or Sams pharmacies, probably even Wal-Mart I believe I have read here. If you live in a warmer climate you can have them shipped. Thriving Pets.com is the best/cheapest place to get them in my experience.