Three Weeks to Train for a 5km Run

The last time I ran in any sort of competition was in the sixth grade of elementary school. I remember running so hard I wanted to vomit at the end. Not a pleasant memory. Fast forward to this morning. Every year, our city has the multi sport event called the IceMan. You can register individually or as a team. My dad and sister decided to make up a team but there are five events (a 5km and 10km run, ski, skate and swim) and only two of them. Somehow they convinced my brother to do the skate event and then I got this email from my mom:

Your dad wants to enter the competition as a family...  Do you think you could do the 5 km run? Your sister is training for the 10 km and she said she would be willing to train with you...you have 3 weeks to prepare. What do you think?

Dad – ski & swim

Sister – 10 km run

Brother – skating

??? - 5 km run

I don't know why but I agreed. Tonight I got a call from my sister to set up our first training session. We meet tomorrow morning at the indoor track (with the little ones in tow). How am I going to manage this? Akk! Is there a team support position that I could sign up for instead? I could design matching t-shirts.