How do I validate my form in a modal window? [closed]

I want to validate my form in a modal window? and tried in several ways I validated the form but when I accept it does not return me to the modal window and the information is sent causing a django error, I want to know if field can be validated by field and that I return to the modal window with the error.

This is my form in the modal window.

<div class="modal fade" id="agregarboncheo" role="dialog" data-backdrop="static">
<div class="modal-dialog" role="document">
    <div class="modal-content">
        <div class="modal-header">
            <button type="button" class="cerrarmodal" data-dismiss="modal"><i class="fa fa-close"></i></button>
            <h4> <span><i class="fa fa-plus"></i></span>Nuevo Boncheo</h4>
        </div>
        <div class="modal-body">
            <div class="container-fluid">
                <form class="formatolinea" method="post" name="nregistro">
                    {% csrf_token %}
                    <label>Bonchador</label>
                    <select required="" name="boncheador">
                        <option>Nombre del bonchador</option>
                        {% for obj in bonchador %}
                        <option>{{obj.nombre}} {{obj.apellidos}}</option>
                        {% endfor %}
                    </select>
                    <label>Variedad</label>
                    <select required="" name="variedad">
                        <option>Seleccione la variedad</option>
                        <option>freedom</option>
                        <option>vendela</option>
                    </select>
                    <label>Bonches</label>
                    <input type="number" name="bonches" placeholder="Cantidad de bonches">
                    <label>Unidades</label>
                    <select id="unidades" name="unidades" onChange="mostrarl(this.value);">
                        <option>Seleccione las unidades</option>
                        <option value="12">12</option>
                        <option value="20">20</option>
                        <option value="25">25</option>
                    </select>
                    <label>Grado</label>
                    <select required="" name="grado">
                        <option>Seleccione el grado</option>
                        <option>40</option>
                        <option>50</option>
                        <option>60</option>
                        <option>70</option>
                    </select>
                    <label>Lámina</label>
                    <select required="" name="lamina">
                        <option>Seleccione la lamina</option>
                        <optgroup label="Lamina" id="lamina1" style='display: none;'>
                            <option>Benchmark</option>
                            <option>Golden</option>
                            <option>Microcorrugada</option>
                        </optgroup>
                        <optgroup label="Lamina" id="lamina2" style='display: none;'>
                            <option>Pet Transparante con papel</option>
                            <option>Transparante</option>
                        </optgroup>
                    </select>
                    <button class="guardar" type="submit" onclick="mensajes();"> <i class="fa fa-save"></i> Guardar</button>
                    <button class="cancelar" type="reset" data-dismiss="modal"> <i class="fa fa-close"></i> Cancelar</button>
                </form>
            </div>
            <!-- /.containerfluid -->
        </div>
        <!-- /.modalbody -->
        <div class="modal-footer">
        </div>
        <!-- /.modalfooter -->
    </div>
    <!-- /.modal-content -->
</div>
<!-- /.modal-dialog -->