In Garmin Coach that seems to be the limit. However if you scroll down the page at Garmin Coach you will find another options for 5k. It's created by a company called Full Potential. It's not Garmin Coach.
If you are already an experienced athlete you may edit trainings the way you need.
I had done that for my last marathon. And I'm doing it again for my next marathon in July. It is a 16-week-plan. I found some day trainings were too light some were a little heavy, some were unnecessary to me. I edited them. Deleted those I didn't need, and clicked and dragged from one day to the day I needed more. Changed distances, time, heartbeat, etc. One by one and worked perfectly. Along the weeks I had to edit again some trainings that I saw became light.
Different from Garmin Coach, those trainings are only available in English. I do speak English, but I wanted to read the training in my native language. I also translated all trainings. All done to be read in my watch training calendar. I'm telling that just to show how editable that training is.
