html inputs in a form doesn't match in the width

i have a form within a panel in my html using bootstrap and it seems like all my panels are well adjusted except for the one which has date and the one used to upload files in it. they have more width than the other form groups because of the button next to them. so my question is how can i modify it to get the same width as the other form groups.

<div class="  col-md-6 col-sm-6   ">
  <div class="panel panel-default">
      <div class="panel-heading">
        <div class="row">
          <div class="  col-md-3 col-sm-3 col-xs-3  ">
             <font size="4" ></font>
          </div>
          <div class="  col-md-8 col-sm-8 col-xs-8  ">
             <font size="6" >إضافـــــة أرشيــــف </font>
          </div>
        </div>
      </div>
    <br>
    <form class="form-horizontal" id="form" action="/insertArchive/" method="post"  enctype="multipart/form-data">{% csrf_token %}

      <div class="form-group">
        <label class="col-sm-4 control-label">إســـم اﻷرشيف</label>
        <div class="col-sm-6">
          <input type="text" class="form-control" name="name" id="name">
        </div>
      </div>

      <div class="form-group">
        <label class="col-sm-4 control-label">الرقم اﻹشاري</label>
        <div class="col-sm-6">
          <input type="text" class="form-control" name="ref_num" id="ref_num">
        </div>
      </div>

      <div class="form-group">
        <label class="col-sm-4 control-label">تاريخ اﻹصدار</label>
        <div class="col-sm-6">
          <div class="form-group">
            <div class='input-group date' id='datetimepicker5'>
              <!-- data-date-format="dd MM yyyy" data-link-field="dtp_input2" data-link-format="yyyy-mm-dd" -->
              <input type='text' class="form-control" data-date-format="YYYY/MM/DD" name="real_date" id="real_date">
              <span class="input-group-addon">
                <span class="glyphicon glyphicon-calendar"></span>
              </span>
            </div>
          </div>
        </div>
      </div>

      <div class="form-group">
        <label class="col-sm-4 control-label">المجلد</label>
        <div class="col-sm-6">
          <select class="form-control" name="section_id" id="section_id">
            {% for sectidon in list %}
                <option value="{{sectidon.id}}">{{sectidon.name}}</option>
            {% endfor %}
          </select>
        </div>
      </div>

      <div class="form-group">
        <label class="col-sm-4 control-label">ملاحظات</label>
        <div class="col-sm-6">
          <textarea class="form-control" rows="3" name="text" id="text"></textarea>
        </div>
      </div>

      <!-- test -->
      <div class="form-group">
        <label class="col-sm-4 control-label">الملحقات</label>
            <div class="contacts col-sm-6">
                <label>إصافة ملف :</label>
                    <div class="form-group multiple-form-group input-group file">
                        <input type="file" name="file[]" class="form-control" >
                        <input type="text" name= "file_name[]" class="form-control" >
                        <span class="input-group-btn">
                            <button type="button" class="btn btn-success btn-add">+</button>
                        </span>
                    </div>
                </div>
            </div>
      </div>
      <!-- test -->

      <div class="form-group">
        <div class="col-sm-offset-2 col-sm-10">
          <button type="submit" class="btn btn-primary">حفـــظ</button>
        </div>
      </div>

    </form>
  </div>
</div>