Voluntary Termination of Car and Reasonable Condition

[Merlincat]

I'm planning on voluntarily terminating my HP car agreement. I've paid well over the stipulated 50% amount and had scratches fully repaired to new. There a couple of very small nibbles on the bonnet where small stones have made tiny chips.

What can be considered as having "taken reasonable care of goods"? The contract says if I do this I will not have to pay any more.