There’s nothing inherently wrong with applying to T20 schools but It’s better to understand the probability outcomes before you apply than be disappointed later.
As many have stated, the chances of a T20 school with a bad calculus grade in your junior year with record amount of applications probably does not bode well for a CS major.
Maybe you should try Rice because you dont have to declare an intended major until your sophmore year or a LAC with an open curriculum?