In the mini-calendar preview in top left, only the numbers (the text) is clickable. So you if want to click on number 4, for example, there's a lot of white space that is not clickable and only a part of the cell - the very number 4 - is clickable. That forces you to be pixel-perfect to be able to switch the week.

Please make the whole cell/row of cells clickable, including the cell whitespace.