具有 width:100% 属性的 div 右侧的空白区域

body {

    background-image:url(images/background-awcc.png);
    background-repeat:no-repeat;
    background-size:100%;
    background-attachment: fixed;
    background-position: center; 
    padding: 0 !important;
    margin: 0 !important;

}

/* Top Menu All Pages */

.topmenu {

    padding:30px;
    background-color:rgba(55, 21, 21, 1);
    border-right:solid rgba(55, 21, 21, 1);
    margin-left:-9px;
    margin-top:-9px;
    text-align:center;
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    box-sizing : border-box;
}

.topmenulink {

    padding:30px;
    color:antiquewhite;
    text-decoration:none;
}

.topmenulink:visited  {

    text-decoration:none;
    color:burlywood;

}

.topmenulink:hover  {

    background-color:darkgoldenrod;
    color:black;

}

    <div id="wrapper">
        <div class="topmenu">

            <a class="topmenulink" href="myaccount.php">My Account</a>
            <a class="topmenulink" href="appointments.php">Appointments</a>
            <a class="topmenulink" href="tutors.php">Tutors</a>
            <a class="topmenulink" href="clients.php">Clients</a>
            <a class="topmenulink" href="schedule.php">Schedule</a>
            <a class="topmenulink" href="statistics.php">Statistics</a>
            <a class="topmenulink" href="help.php">Help</a>
            <a class="topmenulink" href="logout.php">Logout</a>

        </div>
    </div>