Have no fear. The size isn't important. I can see someone getting used to time and temp based on a certain size. But that doesn't mean that 2 pounds less is impossible to get right. Trust your process and don't panic. Probe tender is the same regardless of size. I've cooked hundreds, maybe even close to a thousand over 20 years. For 10 or so years I had no idea what a choice brisket was. Some say you can't make a select or ungraded one tender. That's wrong too. It might be easier to get a prime right but a select can be awesome too. I can't stress a long rest/hold enough.