This question already has an answer here:
I am travelling in California at the moment under the Visa Waiver Program. I am going to be here until the 9th of December then heading to Michigan for Christmas. I was planning to spend some time in Canada to reset the 90 days but have just heard this isn't possible.
I already have the ticket etc booked, will I have an issue driving back into the US even if I am clearly leaving in a few weeks?