Looks like the plastic bottle created a magnification of the sun. that is a bad sunburn. It probably won't recover below that spot. I would cut it above the spot, re-callus and start again. you can put toilet paper rolls over the cutting to block the sun.

Mike

Yes, very bad sunburn. Mike's right. You should start again.

Next time make sure you either put the soil all the way up to the rim, or cover the trunk in a cardboard roll--like from roll of paper towel or toilet paper.

Don't feel bad, I think we've all made this mistake at least once!