When Frank grabs Sherman's binoculars out of the case, another immediately replaces it, making it look like there are 2, not 1, in the box.
Once Roberta and Sherman manage to close the top of the Batmobile (by accident), Roberta crawls under the dashboard to help Sherman reach the pedals. However, the Batmobile, as shown once they drive away, is clearly a 5-speed manual transmission (Roberta shifts the gear stick into reverse), thus if Roberta simply pressed the gas pedal to escape the Penguin and his lackeys, it would have killed the engine and they would have made no progress.