We have a single entry visa for China as we will be on a cruise ship in March 2013

we are visiting Shanghai first then going to Hong Kong, while in Hong Kong we would like to visit Macau for the day and then return to the ship. Will we be ok or should we have got a Multiple Entry Visa for when we return to HongKong from Macau?. Some folks are telling us that we should have done this. Thankyou