I had the same issue when I first started to pull it back. It would only stay for a few seconds, erect or not. From my experience, I would stay with the spooning method. It looks great on you, and it will leave the under side of the foreskin "sensitive", unless you want to lose that sensitivity as well.
In my experience, the glans eventually changed color and toughened up. It also swelled up more because of being exposed constantly. This helped to keep the foreskin back, but it took a lot of patience and time. I didn't know of any other method back when I was 13. I wish I did cuz I would have definitely experimented. Try wearing tight underwear and try putting your penis in different positions, like up against your abdomen or to the side. This helped me while I was trying to train it back.
I know all guys will respond differently, but that's just my two cents.
Also, one thing I did was at night, I would find a way to pull back and keep it in position all night. I tried all kinds of tape, band aids, a hair band behind the glans (can't be too tight). I think I even tried a form of the coin method back then, and even a hair roller once!. But this was me looking for permanent retraction. Sensitivity was a huge issue, and I always went to bed with a hard on, but I really wanted full retraction so I just suck with it. In the morning, I would love the dry sensation of my glans, and I felt like I was making progress as the exposed glans stayed out longer and longer on its own.