Generate Excel File with specific group of output - php

Question

Can someone or somebody help me with my code or with my SQL execution? I'd like to create an excel file based on a specific group of data based on the event/activity they participated in.
Here is my code:
$program_admin = $_SESSION['username'];
$actvty_ID = $_POST['id'];
//$activitydate = $_POST['activity_date'];
if(isset($_POST['export_in_excel'])) {
$excel_sql = "SELECT *
FROM projectcode pj
INNER JOIN activities ac ON ac.projects_id = pj.projects_id
INNER JOIN participants re ON re.act_id = ac.id
WHERE pj.project_code='$program_admin'
ORDER BY re.id DESC "; //pj.project_code='$program_admin'
$excel_result = mysqli_query($connect, $excel_sql);
if(mysqli_num_rows($excel_result) > 0) {
$excel_output .='
<table class="excel_table" style="font-family:Calibri; border:1px solid #1f004d;">
<tr><td></td></tr>
<tr>
<th style="text-align:center; font-weight:bold; border:1px solid #1f004d;">No.</th>
<th colspan="2" style="text-align:center; font-weight:bold; border:1px solid #1f004d;">Name</th>
<th style="text-align:center; font-weight:bold; border:1px solid #1f004d; ">Age</th>
<th style="text-align:center; font-weight:bold; border:1px solid #1f004d; ">Gender</th>
<th style="text-align:center; font-weight:bold; border:1px solid #1f004d; ">City/Municipality</th>
<th style="text-align:center; font-weight:bold; border:1px solid #1f004d; ">Province</th>
<th style="text-align:center; font-weight:bold; border:1px solid #1f004d; ">Contact No.</th>
<th style="text-align:center; font-weight:bold; border:1px solid #1f004d; ">Email Address</th>
<th style="text-align:center; font-weight:bold; border:1px solid #1f004d; ">Organization</th>
<th style="text-align:center; font-weight:bold; border:1px solid #1f004d; ">Signature</th>
</tr>
';
$no = 1;
while($excel_row = mysqli_fetch_array($excel_result)) {
$excel_output .='
<tr>
<td style="text-align:center;">'.$no.'</td>
<td>'.$excel_row["firstname"].'</td>
<td>'.$excel_row["lastname"].'</td>
<td>'.$excel_row["agerange"].'</td>
<td>'.$excel_row["gender"].'</td>
<td>'.$excel_row["city_municipality"].'</td>
<td>'.$excel_row["province"].'</td>
<td>'.$excel_row["mobileno"].'</td>
<td>'.$excel_row["email"].'</td>
<td>'.$excel_row["org_office"].'</td>
<td></td>
</tr>
';
$no ++;
}
$excel_output .='</table>';
header("Content-Type: application/xls");
header("Content-Disposition: attachment; filename=Attendance Sheet.xls");
echo $excel_output;
}
}
And here is the sample output of my code:
enter image description here