Just get better at math / physics if you believe that you are not good at them and it prevents you from studying engineering (that is if you want studying engineering). Everybody has something that they are not good at. This is NOT a reason for getting grade below A, not at all. If you want engineering and want medicine, just do the work and get those As to get high college GPA.
"Also, out of curiosity, is it feasible for premeds to double major? " - ALL of D’s pre-med friends graduated with combo of major(s) / minor (s), but none of them were in engineering. Examples: Zoology (major) / Art (minor), triple major - Zoology / Spanish / Latin Study, Zoology major / Music Composition minor (my D.). D. actually had 2 minors, but had to drop one being 2 classes short of completion.
Anything is possible, but I do not know if you could combine engineering with other major / minor. All around D. also had jobs and had most ECs done during school year. The benefits of it - nice, free summer.
In general, when you face any challenges, cool down and develop a plan. No reason to go crazy and without a plan that has little steps on how to accomplish your ultimate goal (any goal!), challenges tend to overwhelm us (everybody!). You are not an exception here. So, this is my biggest advice which I also repeated numerous times to my D. However, this plan should not be an obstacle is trying something that is not in your plan. Being open and spontaneous is part of life. Nobody can tell you if it is feasible for YOU to be a pre-med and double major. Just try and see how you handle it. Does not work, drop one. Having 2 minors was OK for my D. until one of the Med. Schools added requirements after D. applied. So, she had to drop one of her minors to take classes to satisfy additional requirements. Ironically, while she was accepted there, she turn down this Med. School. And here is another advice - never regret what you have done in a past, cannot turn time back, cannot change what you did, so just learn from your experience.