A couple of days either way won't make much difference. Make sure you start her on a course of worming for pregnant bitches, so the pups get a good start.
av. pregnancy is 63 days but this is actually from ovulation not the 'tye' so have to just take your best guess i'm afraid unless you used an ovualtion detector. like humans some are still delivered early or late. if bitch not settled or you're fussing around her she may try to hang on.