The term centripetal has nothing to do with a hundred petals but from the Latin words centrum and petere, meaning ‘centre’ and ‘to seek’, meaning the movement of something from the edge to the centre. We are all familiar with the idea of centrifugal force (from fugere – to flee), where things are flung away from the centre and this is the opposite.
But in the case of plants it refers to the opening of flowers in an inflorescence, from the centre first, towards the centre. You can see this in lots of cases but it is easily seen in a sunflower where the tiny flowers in the head start to open at the edge and eventually those in the centre open. You can always tell which are the open flowers by where the bees are working.