You should be able to add as an attribute of the TemplateField, e.g.
<asp:TemplateField ItemStyle-HorizontalAlign="Center" ...></asp:TemplateField>
Or, in code behind, you can set it e.g.
gvAgency.Columns(N).DefaultCellStyle.Alignment = DataGridViewContentAlignment.MiddleCenter
replacing N with whatever the appropriate column number is