Accidentally fed my baby mixed milk! 😩

Ok so I was not aware that when you pump throughout the day and mix both old milk and new milk together (only milk pumped in same day) that you had to first cool down the newly pumped milk in the fridge before mixing it into the previously cold pumped milk that was already in the fridge. I fed my baby this and I am so scared now!! She is 6 weeks old. This was 3 hours ago and she seems fine till now. What can happen 😩 google doesn't say!! I am freaking out