Depending on how your school grades Shelf exams, it may not matter. If they compare your grade to students in previous years that also had surgery during your block, then you will do fine. If they compare it to the class as a whole, then you may be at a disadvantage since Surgery Shelf is mostly easy Internal Medicine questions but you will certainly not fail. You can learn most of what you need to know on the shelf from good resources. I had Surgery first and did well.
I had surgery first and did well as well. I actually think it's a good one to start with because they're expectations for students are low and you have to know surprisingly little for the rotation.
The shelf is probably the hardest part, but I think it's do-able with the right resources and effort.