Hi - I used to have palpitations like you describe when I was young. Tests always came back ok. Later in my 30s I had palpitations that would not stop - several times a minute and not letting up. First I thought to move around, did some light housework, etc, didn't make a difference. So then I thought to lay down. While I was laying down I felt like I was going to pass out (more than a headrush). I jumped out of bed and put my head down (natural reflex I guess). I didn't pass out, but I knew I had to get to the ER. When they hooked me up they could see I had something abnormal going on and they admitted me. Eventually I saw an electrophysiologist and an attack of feeling like passing out happened right in front of him. My pulse jumped up to over 300 BPM, then went back to normal. This kept happening to me and scared the crap out of me. Nothing they gave me made it stop - just slowed it a bit. I was diagnosed with VT and implanted with a defibrillator.
Later, my daughter began complaining about similar feelings as you describe while sitting in class. Same thing, all tests came back ok. Even with my history they were sure she did not have a heart issue. The tips were - drink plenty of fluid every day, take magnesium supplement - and my advice, if you drink alcohol/caffeine - don't.
In my opinion - no, palpitations do not scar your heart. Scarring happens with heart attack.