First set the tabControl1 size mode:
tabControl1.SizeMode = TabSizeMode.Fixed;
Then you need to recalculate the width of the bookmark title:
tabControl1.ItemSize = new Size(tabControl1.Width / tabControl1.TabCount, 0);
Please note: 1. A value of 0 means that the height will be the default. 2. Recalculate the size of the item after adding a bookmark to the tab. Think about what happens when you resize the control.
Jarek source share