I've had a curing issue and I can't figure out why!

I was doing a touch up on the paint, I used the same pots the same pigment and was careful when mixing it I used a new brush from the same pack I'd used the others from and painted it straight onto the tail. For some reason it hasn't cured at all and its so confusing

I had basically finished the ta and I need it an a few days time....it's a complete disaster. Is there a way of fixing it?
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