Fast-fashion retailer Shein fell 10 percent on its long-awaited Hong Kong trading debut Tuesday, having raised US$1.7 billion in a high-profile initial public offering.The flotation comes after the company's plans to list in New York and London were derailed by regulatory scrutiny, but it won approval from Chinese officials in July for the sale in the southern financial hub.However, its shares fell to as low as HK$43.72 soon after the open, compared with its listing price of HK$48.56.The IPO put the company's valuation at around US$26.3 billion — well short of the nearly US$100 billion during private fundraising rounds in…