First off your penis is of average size and since you're still young, may still grow more. Flaccid size is difficult to measure as it varies easily with temperature, pressure, etc. Some guys seem to be afraid to show women their flaccid penis because they think it's small. However, a woman isn't really going to care and will come to learn that flaccid size is not a valid indicator of erect size.
You can't go through life being afraid of showing your penis to women you'd otherwise like to get intimate with. She has insecurities too, and trusting each other and being able to relax with each other is part of what makes you like each other. So please don't let your size insecurities prevent you from living life, especially since you're average.
I don't believe stress has ever been shown to have an affect on growth in any form, let alone penis.
The stiffness of your erection depends on your arousal, so it's natural to be more aroused by an actual woman as opposed to porn.
Most guys will ejaculate quickly when first becoming sexually active. It's normal and something nearly every guy has to go through. Girls will understand.