Double buffering Custom control

i created a custome control that draws alot of boxes with text in them uisng GDI, I also implemented a custome scrolling, so when the user tryies to scroll i actually move the panel that contains drawing up and down.

i get alot of flicker while scrolling, i tried using double buffer techniqes but it seems to be to slow or i'm doing some thing worng,
here is the code that uses GDI to draw:


private void DrawProgram (ProgramDetail _program, int channelY)
            {
                  Bitmap offScreenBmp = new Bitmap(_program.ProgramSize.Width, _program.ProgramSize.Width);
                  Graphics GrapoffScreenDC = Graphics.FromImage(offScreenBmp);


                  Rectangle rc =  new Rectangle(new Point(XMargin , YMargin),new Size(_program.ProgramSize.Width - (XMargin * 2) ,_program.ProgramSize.Height-(YMargin * 2))) ;
                  DrawRoundedRectangle(_program.BackColor,rc,MyGraphics);
                  
                        MyGraphics.DrawString(_program.Cat,NoteFont,ProgramBrush,SideMargin + PicDim + SidePicMargin +  _program.LocationX,TopMargin + BetweenMargin + ProgramFont.Size +channelY);

                        
                        //Draw Title Text
                        MyGraphics.DrawString(_program.Title,ProgramFont,ProgramBrush,SideMargin + PicDim + SidePicMargin+_program.LocationX,TopMargin+channelY);
      
                  MyGraphics.DrawImageUnscaled(offScreenBmp,_program.LocationX,channelY);
                  MyGraphics.Dispose  ();
                  offScreenBmp.Dispose();
                  GrapoffScreenDC.Dispose  ();


            }