It would be a shame to say I knew better ... after the fact.

Always wear a helmet when riding. The human skull can be damaged in a natural fall, add 14 - 20 mph to the equation, asphalt or gravel, and complicate it proximity to moving automobile and it is dangerous enough. Reduce the seriousness with a helmet. Concussion, broken collar bones, and scrapes will heal. Permanent damage is what you need to prevent.
I took a tumble with other experienced group riders a month ago. I'm told there was nothing I could have done and it wasn't my fault. The scapes are nearly all healed. The styrofoam broke all the way thru in 1 place and cracked 1/2 way thru in another. After I got our location wrong 3 times and not being able to remember my home phone they would not let me ride to start point. Also have ICE (In Case of Emergency) contact information on you.
6 1/2 miles or 6 1/2 blocks ... wear your helmet ... ride longer.