Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh

 

If you vowed to fast 100 days, you cannot count the 30 days of Ramadan in it unless at the time you had that in mind.

So, you should fulfill your vow.  We are obligated to fulfill our promises and pledges.

 

If you are unable to continue to fast for genuine reasons, then you ought to expiate for it by feeding ten poor persons.

 

Allah says in the Qur’an:

 

{Allah will not take you to task for oaths which you may have uttered without thought, but He will take you to task for oaths which you have sworn in earnest. Thus, the breaking of an oath must be atoned for by feeding ten needy persons with more or less the same food as you are wont to give to your own families, or by clothing them, or by freeing a human being from bondage; and he who has not the wherewithal shall fast for three days [instead]. This shall be the atonement for your oaths whenever you have sworn [and broken them]. But be mindful of your oaths!’ [104] Thus God makes clear unto you His messages, so that you might have cause to be grateful.} (Al-Ma’idah 5: 89)

 

Almighty Allah knows best.