Where did you get the spores? Usually, it's best to use spawn (mycelium) instead of spores to inoculate a large amount of grain substrate. In fact, with oysters, it is often easier to use stem butts instead of spores to get a culture going on cardboard, then you can cover the myceliated cardboard with fresh, moist sawdust or woodchips. Often, grain in a bucket will grow lots of contaminants if you are not careful about sterile techniques. Check out the books by Paul Stamets and the other oyster mushroom threads on this site for more help- especially the one about growing oyster mushrooms on phonebooks. Good luck!