HTML email

I am trying to send the email by HTML format. I got the email working but I couldn't format the output. I would like the output to be centered. Here is my code:

CREATE PROC [dbo].[email_test]
@start_dt datetime,
@end_dt datetime,
@opo varchar(10)

as
SET NOCOUNT ON

TRUNCATE TABLE email_test

INSERT INTO email_test
EXEC dataload.dbo.call_main_proc @start_dt, @end_dt

DECLARE @tableHTML NVARCHAR(MAX)
DECLARE @subject varchar(70)

SET @tableHTML =
N'<table border="1">' +
N'<align="Center">' +
N'<th>OPO</th><th>Col1</th>' +
N'<th>Col2</th><th>Col3</th><th>Col4/Time</th>' +
N'<th>Col5</th><th>Col6</th><th>Col7</th>' +
N'<th>Col8</th><th>Col9</th><th>Col110</th>' +
N'<th>Col11</th><th>Col12</th><th>Col13</th>' +
N'<th>Col14</th><th>Col15</th>' +
N'<th>Col16</th></tr>' +

CAST ((
SELECT
td = [col1], '',
td = [col2], '',
td = [col3], '',
td = [col4], '',
td = [col5], '',
td = [col6], '',
td = [col7], '',
td = [col8], '',
td = [col9], '',
td = [col10], '',
td = [col11], '',
td = [col12], '',
td = [col13], '',
td = [col14], '',
td = [col15], '',
td = [col16], ''

FROM email_test WITH (NOLOCK)
FOR XML PATH('tr'), TYPE
) AS NVARCHAR(MAX) ) +
N'</table>' ;

SELECT @subject = 'Monthly Report : ' + convert(varchar(10), @start_dt, 103) + ' - ' + convert(varchar(10), @end_dt, 103)

EXEC msdb.dbo.sp_send_dbmail
@recipients='test@email.com',
@subject = @subject,
@body = @tableHTML,
@body_format = 'HTML' ;

I was able to center the header but I was unable to center the results. Can someone help on this please?

Thanks.