why's the anchor property of the dgv doesn't work with arrays ?

Question

i have set the anchor property of datagridview to top,left,bottom,right and scroll bars to both and changed nothing in the property of dgv and then used arrays to create columns [by just dgv.columns.add(arr[r,c]);

the columns were created uptill this was fine

 

but when used with large deta suppose just 50 columns and 100 rows it collapsed . the dgv exceeded the borders of the form . why ? i have also coded the hscrollbar like this

 

in the form class i just added the arrar to the dgv and wrote

class form ()
{
       hscrollbar hb=new hscrollbar();
      private void form_load()
      {

          //added the array to the datagridview by
            string arr=field [r,c];  // the values of field is taken already and that's okay .....
            dgv.columns.add( arr,arr);
            hb.scroll +=hb_scroll;
      }
      void hb_scroll()
      {
           for(int i=0;i<dgv.columncount;i++)
           {    dgv.columns[i].headertext= field[r,c];   }
 }