Hadith on staying awake on the nights of Eid

Q:

عَنْ أَبِي أُمَامَةَ رضي الله عنه عَنْ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ : (مَنْ قَامَ لَيْلَتَيْ الْعِيدَيْنِ مُحْتَسِبًا لِلَّهِ لَمْ يَمُتْ قَلْبُهُ يَوْمَ تَمُوتُ الْقُلُوبُ رواه ابن ماجة

Is this Hadith correct? Can we attribute it to the Nabi (sallallahu alaihi wasallam)?

Repenting for one's past sins

Q: I have a personally sensitive issue. When I was a teenager, I engaged in inappropriate sexual touching with a few girls one of whom was my cousin while she was sleeping. Now that I'm an adult and a bit wiser, I feel terribly guilty. I have apologized to my cousin but without telling her what I did. How can I find peace?