Hello and welcome! Also congrats! :)
i never had any spotting from the endometrin, but I know others have had spotting or even bleeding and everything went on to be fine. I would make sure you aren't sticking it up too high...getting it right up by your cervix can irritate what may already be a sensitive spot. Those tablets aren't exactly soft and squishy.
I had mild cramping for the first few weeks, and that seems pretty common, though it freaked me out. Your beta more than doubled, so that is a good sign. Even if you weren't out of town, there isn't really much they can do/tell you other than more betas. (Sometimes you can do a beta at an oit of town lab...maybe ask your nurse if this is a possibility?) I would try not to worry, especially if it stays light spotting. Hopefully you will get some reassuring news at your next appointment! :)