Just because eine plant is bigger then the other doesn’t mean there is a “deficiency”. Just like your brother may be taller then you plants have differant “phenotypes”. Even if they were the same strain they wouldn’t look exactly alike.
You’re feeding what’s needed (really wouldn’t use the bloom again though until you see flowers). Don’t over think growing plants. You dont need mylar however it will help capture more photons. Because you only have 2 plants I wouldn’t even worry about it. I’ve got almost the same light as a veg light on my bubblegum right now and I have Grey painted walls no mylar at all.
Check out my grow log under that light and check the size: Pinkleberry x Black Widow 7/31
Fear not my young friend you’re learning valuable information that will serve you for decades while your friends have to hire someone else to do what you already know 