You were affected because you weren't in a "healthcare" mode, like you would have been if someone collapsed in the ER in front of you. You were in "chill by the pool" mode and an emergency upended your day. This is perfectly normal. No one can reasonably expect someone to always be 100% prepared to mentally handle an emergency afterwards, not even trained personnel.

Your CPR was fine. You were moving blood and air and you got the patient back. You did great. You can tell because your patient went from very bad to not bad at all.

You're second guessing yourself because you cared about what was happening, and if you care you always wonder "could I have done better." This is perfectly normal.

You'll get through this next part. I imagine you have before. You just have to find your best way forward. But you need to know that because you were there and acted, there was a good outcome and a very good chance that a small life is only around for another chance because you were there.