High Erection Angle

My erection points up towards my belly button (it’s not curved, just a high angle). Would a downward erect stretch help improve flexibility?

I had the same issue when I was much younger.
I did downward erect bend and stretching and ultimately injured myself. I healed and my erection angle is now straight out with an upward curve. I don’t recommend trying it out. If you do, expect “ligament popping” and possible tunica injury depending on how you perform the exercises.

Would it be fine if you only do it for around 10 seconds per stretch and very gently?

It’s your cock. Pay attention to any signs of discomfort… or not. There’s a saying FAFO . lol
Be safe.

"Angle of erection" is basically a factor of age. If you’re feeling lazy, you could just wait.