وعنه أن رسول الله صلى الله عليه وسلم قال: "إن في الجنة مائة درجة أعدها للمجاهدين في سبيل الله ما بين الدرجتين كما بين السماء والأرض" ((رواه البخاري)).
I thought Jannat, in general, had 100 levels,
This hadith states that those who struggle have 100 levels of Jannat.
بِسْمِ اللهِ الرَّحْمنِ الرَّحِيْم
In the name of Allah, the Most Gracious, the Most Merciful
This hadith is clear in stating that those who strive in the path of Allah have 100 levels in Jannah. However, there are other ahadith that indicate that there are more levels in Jannah and other ahadith that mention that in general there are 100 levels in Jannah.
One hadith that indicates that there are more levels in Jannah is the hadith where the reciter will be told to recite, and whence his recitation stops is where his level in Jannah will be.
Imam Ibn Al-Qayyim brings all these narrations in order to reconcile between them, he writes after bringing the narration you quoted in the question the following:
“Either these hundred levels are under one level (of the hundred levels) of Jannah, or within each of the general levels there are specific levels within them and these hundred serve as the last hundred.”
Only Allah knows best
Written by Maulana Imran Mughal
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Imam Ibn Al-Qayyim, Hadi Al-Arwah (Dar Alam Al-Fawaid), 1:157.