I looked into this a little more, mainly out of curiosity.
The gestation period typically runs from 57-69 days:
"The second question is easier to answer than the first; a queen's gestation period typically runs from 57 to 69 days, with the average of 63 to 64 days. I like to use "63," because it is nine weeks, equating to human pregnancy average of nine months, making it easier to remember. Of course, your queen will have her kittens when she is going to have them, so these figures are only for your benefit, to be able to approximate the time. "
Maybe it is too early to be worrying? But if you really want to make sure all is ok, do as jules has suggested and give your vet a call.