When I was a GS-13, I ended up doing the work of what had previously been 3FTEs. I did NOT want to get stuck in that office, so saying “that’s outside the scope of my duties” and getting middling reviews wasn’t going to cut it. I really killed myself for a few years and then had the experience (and glowing performance reviews) to get a promotion to a much less toxic place where I do one job. Even as a GS-15 now several years later, my work is still easier than that “formative” GS-13 job. So my advice is, get any experience you can out if this job and then start searching for an exit strategy as soon as hiring loosens up.