The mini cart is already on the product page. It is visisble on every page.
The blue box?? are you referring to the product variations selection area?
If so, the size of the box is determined by how many different types of variations the product has.
For example, you have Colors (Cores in Portuguese). If you also had variation options such as Sizes or Weights then the box would be bigger to accomodate these options.
I hope I have understood your questions correctly. Please let me know if not.