The first set of parks were available for booking Monday morning. The government says the high volume of campers going online to nab sites quickly contributed to a processing error.
"I was advised that the difficulty lay between the reservation system and interfacing with the financial processing system. At some point in time during the peak times, they stopped communicating with each other as they should have been," Parks Minister Kevin Doherty said Wednesday.
Approximately 7,000 reservations were completed, but about 1,500 people were charged more than once for their campsites.
Doherty couldn't say how much they were over-charged.
"I don't know the extent of what the largest bill may be. Depending on whether you're trying to book a site for the entire summer, if you're trying to book multiple sites for family members, there could be a significant cost with respect to what's being charged to your credit card," he said.
"We're just asking individuals to take a look at their credit card statement as quickly as they possibly can, and if there are inappropriate charges on there, or charges that they don't think match up with what they reserved, let us know. We're going to work with them as quickly as we can."
The minister said the system had been tested based on the number of bookings last year. It appears more people used more devices — including computers, tablets and smart phones — to get on the site this year, he said.
The company that handles the bookings was surprised by the demand, Doherty added.
"What they're telling me is they did not anticipate this kind of volume."
The problem appeared to be fixed in time for Wednesday's bookings. The government said about 3,400 people made camping reservations in 90 minutes Wednesday morning and there didn't appear to be a problem.
Another set of parks are to be made available for booking Friday morning. Doherty said those bookings will be spread out over three days.