You have it backwards. Trying to be a doctor is no safety net at all - it’s very hard to get into medical school and the majority of premeds change their mind. You think you have biology figured out? So does everyone else in your biology classes, and if the class is graded on a curve you all won’t be able to get an A. As a result of the vast numbers of don’t-want-to-be-premed-anymore biology majors, the job market is much harsher for a biology major (or any related major) than it is for any engineering major.
Engineering is a lot of work, so if you want to realistically double major count on spending at least 5 years in undergrad (possibly including summers). You can simply minor in another subject instead. Or you can just take random classes that interest you instead of declaring a major or minor in the subject - in most cases, you don’t have to major in a subject to take classes regarding that subject - you just need to take the prerequisite classes.