You should be able to get the dynamics you need using the damper pedal. If you don't have a damper pedal or it is still not quite enough you can relatively play the other parts of the piece louder.

Dynamics in any piece are relative. You don't need to play them at an exact dB level and it is very often that a _p_ or _pp_ in one piece isn't the same exact as in another piece. Because of this just make sure you play the quietest part the quietest and the loudest parts the loudest.