var workbook = new XLWorkbook();
var ws = workbook.Worksheets.Add("Margins");
ws.PageSetup.Margins.Top = 1;
ws.PageSetup.Margins.Bottom = 1.25;
ws.PageSetup.Margins.Left = 0.5;
ws.PageSetup.Margins.Right = 0.75;
ws.PageSetup.Margins.Footer = 0.15;
ws.PageSetup.Margins.Header = 0.30;

ws.PageSetup.CenterHorizontally = true;
ws.PageSetup.CenterVertically = true;

workbook.SaveAs("Margins.xlsx");