You might have divided opinions but that’s because people are giving you what they want the truth to be.
Under Section 9, goods must be of satisfactory quality, taking into account their description, price and all other relevant circumstances. However, ordinary scratching of a relatively soft precious metal through normal wear does not necessarily constitute a fault or a failure to meet that standard.
Section 20 provides a right to reject goods where the relevant statutory requirements have not been met. However, the short-term right to reject under Section 22 is not an unconditional 30-day returns policy. You must first have grounds to reject the goods, such as a failure to meet the satisfactory quality requirements under Section 9.
There is no general legal obligation for a retailer to explain every characteristic of a material before purchase. The fact that 18-carat gold is relatively soft and susceptible to scratching does not automatically make it unsuitable for its intended purpose, nor does the absence of a specific warning establish a breach of consumer law.
Section 19(14) establishes a presumption that a failure to conform discovered within six months was present at delivery, unless the retailer establishes otherwise or the presumption is incompatible with the nature of the goods or the failure. However, this does not mean that any damage discovered within six months is automatically considered a manufacturing defect. There must first be an identifiable failure to conform to the contract.
You have acknowledged that you wore the ring after purchasing it and only subsequently noticed the scratch. While this does not establish that you caused the damage, neither does it demonstrate that the ring was defective or damaged when supplied. If anything it implies that the damage was done when wearing.
If the ring were abnormally fragile, had a manufacturing defect or was demonstrably damaged at the point of sale, you could potentially have grounds for a claim. However, on the information provided, you have not established that the ring fails to meet the statutory requirements, so have not established a legal entitlement to reject it and demand a refund.
Let them polish the ring, it’s your best/only option