Firstly I assume you have successfully using the PST visually with an eyepiece to see the chromosphere – although solar activity has reduced recently there is a reasonable group at the moment which even produced a flare this afternoon. So if all is OK using the PST visually this indicates that you have correctly wavelength tuned the telescope. If it off-band you will just see a featureless disk a bit like in your image.
The difficult part of using a DSLR or indeed any other type of camera with a PST is obtaining focus. This requires using a Barlow lens (which you appear to be using) or an eyepiece lens to bring the focal plane of the DSLR closer to the PST eyepiece holder. I suggest you perform a Google search using ‘PST and DSLR’ without the quotes. There you will find videos and other information (e.g. https://www.youtube.com/watch?v=RYDzdYkVbGM). Note there is no need to modify the PST eyepiece holder itself.