Hello, thank you for your response. I was able to solve the issue and use the spline arc as I had it by connecting the two cloners making up the blood vessels. I appreciate your time.

@Dr-Sassi The arc is created at 4:30 and the spline wrap is created at 5:00. I apologize for not including time codes in the original post! Here is a dropbox link with my file included: https://www.dropbox.com/s/nhav5p0lox5nukf/BloodFlow_1.c4d?dl=0
I have tried every axis and attempted to adjust the bounding box as well, but I may be adjusting it incorrectly.
I'm attempting to create the blood vessel that the blood cells flow through. I have successfully created the red blood cells.

I'm trying to follow this tutorial: https://vimeo.com/170335543 and am having an issue with the spline wrap. It's not following the reference arc, and no matter how I adjust the hierarchy, axes, radius, etc. I can't get it to work. I've deleted it and recreated it multiple times.