I was actually working with the same code as you posted. The idea mainly is to multiply the number of controls with 75, then get the distance, that is number of controls minus 1 multiplied by the distance 200.

The result of this is subtracted from the form's width. Then divided by 2.

But the starting point of the first image control is not right. Giving me the value 337, when it should be 275.

I got 275 by manually centering the controls horizontally using that in the layout toolbar.

Could the error be because of the form's width?