从 MySQL 下载二进制文件作为可执行文件

Question

    include_once 'dbconnect.php';

    $query = "SELECT * " . "FROM download WHERE username = '" . $username . "'";

    $stmt = $conn1->prepare($query);
    $stmt->execute();
    $result = $stmt->fetchAll();
    $blob = $result[0]["File"];

    header("Content-type: application/octet-stream");
    header("Content-Disposition: attachment; filename=download.exe");
    header("Content-length: " . strlen($blob));
    echo $blob;

I have this code, when it downloads the executable is only 1 MB while the file should be 13 MB