score:2
The TN visa requirements for Canadian and Mexican citizens aren't quite the same since Canadians don't need a B1/B2 visa, and can receive a TN visa at the border.
What is clear, however, is that if you are still employed on the date that you return from your trip, you must enter on the TN visa.
My understanding is that you are supposed to leave the country by the date your TN expires, and you can't stay longer unless you file to extend your status. For Canadians, this basically means simply leaving the US and coming back, and if you're in driving distance you could literally do that on the same day. Since you are Mexican and you already have a B1/B2 visa you should probably show it to US immigration and they will tell you what to do. According to the comment, they can't admit you on both statuses simultaneously; I don't know if it's possible for them to admit you on you TN until its expiry, and post-date another I-94 for the B1/B2 admission. If that's not possible you may need to go out and come back in again, so you might need a second trip to Canada (assuming it's close enough.)