I have a 1998 Saturn SC2 White Hot auto with 205k miles. This morning I had to do a U turn since I parked on the road. It shifted fine to drive. The street was narrow, so I had to reverse, which I waited for a few seconds since it takes a bit to get to. When I shifted back to drive, it wouldn't go. I wiggle my gear selector till I heard a click and it went, then my Service Engine Soon light turned on. I scanned it, gave me a stored P0731 code, says its a  Gear 1 incorrect ratio, which i was told to deleted. I'm told that I didn't wait for it to warm up properly. Is that the case or is it much more serious?

I know the transmission is probably on its last leg, but this never happened before and it's pretty good other times.