Can you clarify, "not getting everything you want included"? Are you talking about within the frame borders or in terms of keeping what is needed from front to back within critical focus, aka depth of field?
If the problem is keeping everything within the frame and you are in a working environment where you cannot move further back then as Ray noted you will need a shorter focal length instead of longer. If you are going for a highly blurred background but you have to be too close to the model to completely frame the desire content while achieving the desired background blur, then a faster (wider aperture) or longer focal length lens is what you need.
Try a depth of field calculator to look at various combinations of distance, what is in frame, and the depth within critical focus and this will help you decide what focal length and f stop is needed to fit your work parameters. This one is easy to use and includes typical model coverage settings from face to full body as quick presets in the calculation setup:
https://www.pointsinfocus.com/tools/depth-of-field-and-equivalent-lens-calculator/#{%22c%22:[{%22f%2...}
Don't forget to change the camera/sensor type to APS-C in the calculator if you are using a crop camera.
Rodger
EOS 1DX M3, 1DX M2, 1DX, 5DS R, M6 Mark II, 1D M2, EOS 650 (film), many lenses, XF400 video
