I've been trying to model my toothbrush to practice surface modeling. 

When creating the surface loft, it keeps rejecting any additional guide curves. (pictured below)

Can anyone point out what I might be doing wrong/what's wrong with my build so far?

This is the youtube video I was following, measurements are from my own toothbrush SolidWorks S Tutorial # 276: Toothbrush (advanced surfacing) - YouTube 

Thanks!