Is it the chain or is your rear derailleur not taking up the slack? If you put it in the big chainring and the bike rear cog, is there much slack or can you pull the chain away?
Take it up to Cycleville in Cedarville (Plymouth) right up Rt. 3 from Scussett up by exit 2. See Jimmy the owner and he will fix her up right for you while you wait! Tell him BigFish sent you!!