If you wish to have the text aligned horizontally you need to set the DrawMode to OwnerDrawFixed. Then on the DrawItem event, manually draw the control like:
private void tabControl_DrawItem(object sender, DrawItemEventArgs e)
{
string tabName = tabControl.TabPages[e.Index].Text;
StringFormat stringFormat = new StringFormat();
stringFormat.Alignment = StringAlignment.Center;
stringFormat.LineAlignment = StringAlignment.Center;
if (e.Index == tabControl.SelectedIndex)
e.Graphics.FillRectangle(Brushes.LightBlue, e.Bounds);
e.Graphics.DrawString(tabName, this.Font, Brushes.Black, tabControl.GetTabRect(e.Index), stringFormat);
}