it should especially matter on a fixed gear setup. since the chain is only ever on one ring and one sprocket, the noticible wear will be accellerated. not to mention that the wear happens during pedaling and when applying backpressure.

if the chain is stretched that badly, the op will most definately need to get a new chain, chainring and cog and install them together. a single new part will wear fast and mimic the old wear pattern. a new chain is going to be noisy and rough.