Is that 3/8" elongation over 24 pins or over the entire length of the chain? If it's over a nominal 12" (24 pins) your chain, cogs and chainrings are ruined. If it's over the entire chain (typically ~112 pins) you are just over the normal replacement value of 1/16" in 12" and your chainrings should be fine and the cogs may or may not be.