Blue is the hardener, so if you wanted it softer you’d use more yellow, harder more blue.
If your putty isn’t curing well then it could be a poor mix (green stuff/kneadatite is usually easy to see if it’s mixed as it turns, well, green) or it could be that the putty is quite old and degraded.
Does the yellow and blue look vibrant and bright, like a 90s paintjob, or does it look dull and the blue may have developed a slight brown tinge - like a modern paintjob?
If the latter it’s old or has been exposed to too much light/heat and the hardener may not be doing its job well.
It probably will cure fully but might take longer.