I do feel a notable difference when rolling the R, I am quit used to rolling the R though because its deeply rooted in my native language. Vibrating can be done without rolling the R if it is uncomfortable for you, but if you re able to roll it i would recommend rolling it.
So just roll with whatever your guts telling you, you'll be fine.
Most importantly the results are still there as long as you are focused and do not doubt the work whatsoever.
Vibrating in the correct pitch makes it stronger. So do what you can do comfortably for now and when you have time practice rolling your R's. If a child can eventually do it while trying to mimic motor sounds over and over then it should come naturally over time with enough practice for someone older. Not saying this to be condescending but to show that it's easier than not if one practices enough.
Either way is fine as long as it works for you and as you stated it does. You shouldn't have any doubt in this situation - you're getting the result you're supposed to. Let that fact sink into your mind to replace the uncertainty with belief.
The fourth link on the following page gives examples of SURYA with both R's
https://joyofsatan.org/www.angelfire.com/empire/serpentis666/Aura_Cleaning.html