Unfortunately that is a drawback and you can only specify horizontal or vertical borders (or both) but not individual cells.( border-spacing: 10px 0;/* border-spacing: horizontal vertical */)
The border-spacing puts the spacing inside the columns but also outside the columns so that does reduce the space between the table and the edge of the window (or parent container). Most times you can just drag the parent wider with negative margins by the amount that you set on the border spacing and then all is well.
Remember you only need border-spacing if you have background colours and borders that need to be shown to equalise. If not just put your margins on the inner content instead.
Flexbox can also be tricky to get consistent margins also.