When you’re turning 180 degrees, you’re facing the opposite direction, so “doing a 180” means to change your attitude or opinion to the complete opposite.

Cambridge defines it like this: ”a sudden change from a particular opinion, decision, or plan to an opposite one” <a href="https://dictionary.cambridge.org/dictionary/english/180" rel="noopener noreferrer" target="_blank">https://dictionary.cambridge.org/dictionary/english/180</a>;

”Jack's done a 180 and agreed to come on the trip.”

The song is about being recovered from heartbreak and telling the ex-lover to walk away. She’s indicating that she’s not the same person that she used to be but that she completely changed and is over him.

You might enjoy this video where Dua Lipa speaks the lyrics to her song to complete strangers: <a href="https://youtu.be/yciIVK7n-7Q" rel="noopener noreferrer" target="_blank">https://youtu.be/yciIVK7n-7Q</a>;

Is it like " to do an about face "?

It means to turn completely around so that you are facing in the opposite direction. This can be literal if you find yourself walking in the wrong direction or metaphorical if you have a strong opinion about something and change your mind ( I used to think he was irritating but now...).

The more complete expression would refer to 180 degrees. As in turning 180 degrees.

There are some great comments here already. Let me add a couple of fun facts:

A 180 can as well refer to a basic trick on a snowboard/skateboard/etc, where you complete a 180° turn

How to 180: https://www.youtube.com/watch?v=ATMiAVTLsuc

Also, did you know that 180 is the highest score you can reach playing darts in one turn (3x60)?

Maybe and just maybe, the singer is a big sports aficionado?

(I reckon however, all of the comments below are closer to the truth than sporting is)

To go in the opposite direction, can be literally related to travel, to turn 180 degrees. Or metaphorically regarding a course of action or policy; i.e "The government has done a 180 on it's policy for no tax increases."