Faltaba btn-block

frontend/templates/django_registration/registration_form.html

@@ -76,7 +76,7 @@ You should have received a copy of the GNU General Public License along with thi
                     <div class="g-recaptcha col-sm-12" data-sitekey="{{ data_sitekey }}"></div>
 
                     <div class="form-group col-sm-6 col-sm-push-6 form-footer">
-                        <button class="btn-primary btn" type="submit" id="submit" value="Registráte">Registrate</button>
+                        <button class="btn-primary btn btn-block" type="submit" id="submit" value="Registráte">Registrate</button>
                     </div>
                     <div class="form-group form-group-lg col-sm-6 col-sm-pull-6 font_small form-footer">
                         <p>¿Ya tenés usuario? <a href="/accounts/login/">Ingresá</a></p>