Help controlling dynamics

[Kapellmeister27]

right now i am learning a contemporary piece that is very pointilistic.  It contains one long line of skips about an octave apart up and down the keyboard quite fast.  I have found taht i can be pretty accurate, but there are some times when i need to have dramatic pp subitos.  Usually when playing other pieces this is not hard because my hands are already there so the control is easier.  But when playing this one i have a harder time.  I am all right playing quietly but someimes it is so quiet that the key only goes down a little way and the sound is not made.  Any suggestions on how to fix this?