Many times, pitch events have their own rules or guidelines for the pitch. They may limit the number of slides or even give you a full structure of the pitch that you need to follow. Before the actual event, there may be a session where the pitches are prepared and modified according to feedback from coaches and peers. Time for modifications is often really limited, so don't concentrate on making it as beautiful as possible, rather just testing out raw ideas and see what kind of a feedback they get.