I haven't gone through the application process yet, so take my advice with a grain of salt. If you are completely set on med school and you love both of your majors (in unrelated areas), you should go ahead because it is more likely that you will do well since you are so invested in your classes.
If I had to do it all over again, I would probably just major in humanities and take my pre-reqs and some advanced courses to prove my competence. This would leave me time to hone my extracurriculars. Keep in mind, I would not do it for med school, but for me since my humanities courses have been far more interesting than my engineering classes.
That being said, engineering or any other science, offers you a lot of opportunities that can be hard to ignore. For example, the strong quantitative skills you learn from engineering are easily transferable to research. There are a ton of research opportunities for engineers plus I don't know any engineering major who would take an unpaid internship 🙂 Finally, who can forget a ton of engineering scholarship opportunities (well, not a ton, but compared to other majors...).
So, you get the idea. It's a very personal cost-benefit analysis. And you should make your decision considering all of these factors. I wish you the best of luck, and let me know if you have any more questions!