Perspective is an important thing to learn, and it seems you've got it down pretty good so far.
I actually like how the skatepark turned out.
Some of the other sketches are indeed a bit of with the perspective as you mentioned.
But they are good practice, and you've been able to pin down the problem so that's great.
Keep on sketching mate !
Don't worry about posting finished renders.
This is a "sketch"book forum, afterall. :-)
The forest fight for sunlight, that takes root in every tree.