"We've never had to close two days out like we have done this year."
It comes after Addington Cup Day on Tuesday sold out – tickets there were capped at 12,000.
Mills said he believed the sell-out was due to people being unable to attend events earlier in the year due to the nationwide Covid-19 lockdown.
"When we throw our minds back a couple of months to where the country was, and we had cold water running through our veins about whether we would have the cup meeting," he said.
"We have had the lockdown and the doom and gloom during the peak of the Covid-19 situation and I think it is that natural reaction of let's get out and enjoy ourselves while we can."
He said they had a "record number of fields" for Saturday, with 223 acceptors.
"It's a really positive thing, you know, thinking where we could've been.
"Regrettably if you haven't got a ticket by now you will have to watch through the TV."
The first race is set for 11.05am on Saturday.
