Downstream O2 Sensor

I have the 09 aveo and I have been working on the 02 sensors. My main question is how much of a pain is it for everyone else to screw the new downstream O2 sensor in? I swear to god I've been trying to get it in for about an hour. It was stuck in pretty tight and I was worried that I may have stripped the threads on the aveo taking the old sensor out, but upon inspection it looks okay. Does anyone have any tips on screwing the sensor back in? I am seriously thinking about towing it to a shop to see if they can get it in. If I stripped the threads then that is beyond my means of fixing.

Just a quick history for those curious, I had been getting the codes P0036, P0138, P0140, & P0141. The car had been having some rough idling and the idling was getting worse the longer the car was on. I thought I would change the upstream sensor first, that didn't fix the problem. I realize the codes were indicating the downstream O2 sensor, so I figured I would change downstream sensor. Now I am taking a break for the evening while I figure out how to get the damn sensor in.