Premanand Maharaj Ji

Is everything in my life already fixed by destiny?

Only the fruit is fixed, not your choices

Only two things are fixed: sorrow from sinful karma and worldly happiness from virtuous karma. Whether you do good or bad is left to you.

Two things are fixed: the fruit of sinful action is sorrow, and the fruit of virtuous action is worldly happiness. Only this is called prarabdha.