try below
Dim formatter as StringFormat = New StringFormat()
formatter.LineAlignment = StringAlignment.Center
formatter.Alignment = StringAlignment.Center
Dim rectangle As RectangleF = New RectangleF(0, 0, richTextBox.Width, richTextBox.Height)
Dim font3 As Font = New Drawing.Font("arial", 10, FontStyle.Underline)
e.Graphics.DrawString(Me.RBC_Seriestxt.Text, font3, Brushes.Black, rectangle, formatter)
And check below article as well
Draw Over WinForms Controls[
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