Final Cut Pro problem

Today we began editing the clips together on Final Cut Pro, me and Brittany sat down and applied and discussed where and how the title sequence will fit together. As we started on the mac computers another class came in to use the rest of the macs, this was a problem as Final Cut Pro began to lag and when we tried to watch our footage back it kept missing out scences we need to see, this became a slight situation as today we planned to complete the freaks section at the beginning of the title sequence. This set us back as we wasted an hour waiting for the macs to become faster.