Question How do I do a mandatory pitstop?

I did the following in a test race and finished first, but the game considered me third place after the race:

In open pit time I was in the pit, the car was standing and then I canceled in the menu so no changes were made. After that I continued the race.

Do I have to change anything and if yes, what do I have to do for a valid mandatory pitstop?

 

if there is mandatory pitstop you have to change tires for it to count, or you will lose your position in race after finish..
Don't know if you have to change all though but I always change all

 

Okay... thanks... I wondered why it did not count. I don't know the real race rules...

 

You're welcome I usually missed the pit window totally before, So lately I've been more thorough to check when it is open and made a bunch of presets to pick from depending on race type