Then you must not have the available room on your System OS Partition to do a shrink further. This is possible. You may need to delete something or move it to make more room to shrink. Your size of 529 MB should be enough for the Recovery Partition. You can make it bigger like 1024 MB (this will be 1000 MB) - more than enough. Are you sure you are trying to shrink your OS Main System Partition? How much room do you have on your main OS Drive (usually C:) for data? You should have at least 50 GB. Did you try a shrink using Mini Tool Partition Manager? It is pretty easy to use. Did you verify your reagentc is really working with reagentc /info inside diskpart? You might want to take a screen snip of Create and Format Hard Disk Partition to see what kind of partition size is there.
This is a good video on how to do it: https://www.youtube.com/watch?v=hlNtLcFqfOo