Notification to phone writes multiple lines on group entities should be only 1

I need some help configuring a template. I have a group of 7 door sensors and an automation is fired if any of these open for the first time, which works fine.

- alias: 'Manual - Trigger alarm when doors are opened'                                                                                                   
    - platform: state
      entity_id: group.Door_sensors
      to: 'on'
    condition: template
    value_template: "{{ states('alarm_control_panel.home_alarm') != 'disarmed' }}"
    - service: alarm_control_panel.alarm_trigger
      entity_id: alarm_control_panel.home_alarm  

    - service: notify.mobile_app_XXX
        title: 'Alarm'
        message: >
          {% for entity in trigger.to_state.attributes.entity_id %}
            {% if states(entity) == 'on' %}
              {{ state_attr(entity, 'friendly_name')}} opened
             {% endif %}
          {% endfor %}        

In a notification to my mobile if have the entity that opened listed, but it looks like in the message it writes a line for each other sensor in the group as well resulting in a big ugly notification on my phone.

Can someone help me to just get the one line with the entity that acually opened first?

Replace {% and %} by {%- and -%}.