I literally have no idea what that's a picture of.
It's your bicep. It's entirely normal, it's why you shouldn't play around with bodybuilding poses unless you're a bodybuilder. This "issue" doesn't deserve any of the mental energy you've given it these last few days.
gap, no gap, gap, no gap, gap, no gap, gap, no gap.
You left out a muscle group and I'm guessing it's because you don't train it/them.
You're way too young and way too inexperienced to be physically unable to curl a straight barbell. I'd spend time addressing that instead of "the gap".