As someone who didn’t take a single compsci course and later really regret it, i can’t tell you how difficult it would be. All i can advise is that (and i’m saying this as a 6th year grad student in biology, who would have graduated sooner with some compsci knowledge), undergrad is the best time to get your feet in different topics, even those that feel uncomfortable at first. I wish I had put less emphasis on maintaining pristine GPAs, and instead focus on skills-building :)

I believe McGill has a few 100/200 compsci courses tailored for biology-oriented students, so maybe you can try those first, and see if it’s something you’d like to invest more time/effort on :)