Plastic containers exposed to heat while cooking
You should be perfectly fine.  PET plastics do leach antimony, and the rate of leaching does increase with temperature, but it would take a much longer exposure time to be of any real concern.  You would be putting yourself more at risk by drinking water out of a plastic bottle that had been left in the sun.

Here's a relevant study about water bottles:
Antimony Leaching from PET

The abstract adequately addresses concerns to do with high temperatures and PET.

That said, safety is always the highest priority, and if you notice anything unusual about your soup, it's best to err on the side of caution.