Marathon plan - long run

Hi there, I'm currently training for a marathon in July. I'm in week 11 of 26, wanted to give myself as much time as possible as this will be my first full marathon. Though my monthly mileage as increased throughout the weeks, I still haven't a run longer than 13km in the plan. I just wanted to check if this is normal? And if someone has used the Garmin coach plan, what's the longest run you did during the training block?