I read someone said it is & it was my first time ive known it, but i still have doubts about it.
No it's not true. You can ask for forgiveness once and that can be good enough.
There's no specific number mentioned. May be the person who told you about the 100 times a day thing mixed it with a hadith of the Prophet =
"A cloudiness comes over my heart, I seek forgiveness from Allah a hundred times a day."