Revealing mistake: When Ed falls on his belly and dies of a heart-attack at the end of the film, if you look closely, you can see the actor is still breathing a few times. He's trying to hold his breath, but every so often, you can see his back subtly raise and lower as he slowly takes a breath in and out.
Other mistake: When Gino gets shot and killed, the gun that shoots him isn't being held at quite the right angle... the way it's aimed, the bullet should have gone to the right of him, but instead he reacts as though he's been hit in the head. (Given it's a super low budget movie, they probably just didn't have enough time or money for a second take).