I'd immediately throw out that weight scale, or stash it away in your closet where no one can see it for awhile. Unless a teen is morbidly obese and in danger due to being overweight, a parent shouldn't be so aware of the teen's weight.
Instead of ever again mentioning your son's or your or your husband's height and weight, focus on strengths, character, reliability, kindness, trustworthiness.
Help your son gain some personal power. Many cell phone providers and auto insurance companies have a road service rescue (gas, lockout service, changing a tire). Without making a big deal of it, add that service to your son's insurance or cell phone and just tell him to make sure to call that, not you (tell him you might be at work, and it's time he had his own road service contract).
As for helping carry something heavy, well that's just common sense and kindness. But you can say something like "hey, want a hand with that?" and not point out that you're bigger and stronger. Be matter of fact.
And of course you don't pretend anything. What does that teach? But you DO show him what matters in life. Which is not strength unless you're a professional wrestler. As an ER nurse, of course you need physical strength, but frankly, I'd rather have an ER nurse with compassion and heart and a helpful attitude than one who's able to lift a hospital bed with one hand.
Does your son have any skills, hobbies, interests? Chess, government, computers, technology, animal care, etc? Make sure he has the capability to pursue whatever makes him HIM. Weight is flexible, height is unpredictable, but brain power and personal character can be developed, molded, and they are much more valuable.