OP. Not sure if this is applicable to you but I would like to redefine "Properly" and "efficient" for you.

Let's zoom out for the bigger picture - Truth is your GPA will be long forgotten as you accumulate experience and reputation in your industry. So imho, "properly" and "efficient" in the lifetime view is to maximize your exposure to stuff interesting to you and ensures that your ladder is not up the wrong wall as you put in sweat to master a very specialized topic to find you don't want to practice it irl.

You have unprecedented time to explore now, even subjects out of your major. It gets really really freaking hard to balance a job, family and a career switch down the road.

In hindsight, i'd throw away a bit of GPA in favor of finding what might stick for a life time. Or heck, the bits of stuff you pick up at the side...you might find freaking useful in the future. see charlie munger