I am having a doubt regarding margins in this project I am realizing. Should i consider these triangular shapes when calculating margins, or should I imagine a blank page as I am doing now? Sometimes I have the feeling the shape in the upper right corner comes too close to the text, or the page number in the bottom left; so I thought I could ask you opinion about it. Thank you!
There's no steadfast rule here.
For me, things ultimately amount to visual perception. If the page "feels" cramped due to design elements, then factoring in the elements when considering margins will be beneficial. However if standard margins without considering design elements don't unnecessarily cause any visual "crowdedness" or confusion, then ignoring the elements in terms of layout is fine.
I don't think those particular elements encroach too far into the visual space and I think how the margins are configured and content is placed is fine in your sample.
Unrelated, I would consider reversing the angle of the blue and yellow elements though. As you have them, they convey a downward right movement, which psychologically conveys "melancholy" or "depression". Optimally you want an upward right movement to convey "joy" and "happiness". So, I would possible flop the angles, so the blue is upper left and the yellow is lower right. It is not impossible that it's this psychological impression you are picking up on which is making you uneasy with the layout.
This depends on the entire content you are working with, but, since your spread layout is tilted to the bottom right corner, I would find a way to also tilt the right hand side content.
Optically, the text box on the right sits too close to the blue triangle. I would leave more white space up there, moving the text box either beneath the main headline on the left or flush with the text box on the left.