Yeah I would not worry about it at all, to be honest, and that's very out of character for me to say! Here's why:
1) OR anatomy is not like M1 anatomy. Even if you were the Jedi master of M1 anatomy, OR anatomy presents new challenges.
2) The time required to learn ALL of anatomy to an adequate level AND remember it until M3 will preclude studying much else.
3) You're learning a lot more than you think.
4) The only way to really learn surgical anatomy is to become a surgeon. There's no book you can read or video you can watch - it just takes time.
So give it your all this year and learn everything you can, but learn everything else too. Anatomy pimping is such a small part of the pimpage you will receive, even on your surgery rotation. Oh, and there's that little matter of boards and needing to be ready to crush it in one more year. Trust that you'll have enough time to read before OR cases; you will. If you want to bookmark it for later, here's my quick and dirty method to prep for the OR as an MS3:
1) Know the patient's H&P cold. So cold you could present it from memory. Know the whole story and know WHY you are operating.
2) Find a youtube video of the operation. There are hundreds of these for just about any surgery.
3) Get out netters or whatever atlas you like and pour over it.
4) Find a chapter in a surgery text or a review article about the operation you're doing. Read it. I used to print these and keep copies in my pocket to read between cases. I saw my residents doing this and just kinda picked it up from them.
5) If you have a surgical atlas in your library or available online, see if the procedure is in there. This will help with landmarks and the approach you'll likely use.
6) Google [insert name of operation] pimp questions. There are some classic questions that go with many operations. Know them if you can.
7) Watch a different youtube video and see how much you can identify as you watch it. Pay attention to key points in the case. These are usually the ONLY things in a video as the surgeon has edited out all the in between stuff.
All in all, you can do all of that in about an hour once you get good at it. Maybe a little more for something bigger or if it's your first time seeing a particular case and the anatomy is tricky. Good luck!