What the sample is would be useful too, as well as not cropping the search range off the plot. The plot would indicate that your helical parameters are a long way off optimal and the search range is insufficient, however amyloids are very difficult to optimise helical parameters for without reaching extremely high resolution (<4 Ang).
If the sample is amyloid, @hickschadw recently shared some extremely useful observations here.
If not amyloid, try refining with helical symmeterisation disabled and use a combination of Chimera (for a rough estimate to start) and the symmetry search tool to try to lock in some potential solutions.