There are different systems to write Chinese characters in Latin alphabet such as Wade–Giles and Yale. 'Qin' is the correct spelling in Hanyu Pinyin romanization system which is the official romanization method in China and pretty much the international standart since the early 1980s.

And yes. 'Q' makes a similar sound to 'ch' in Pinyin. But it is different than the sound written as 'ch'. I would say q is softer and ch is harder in pronunciation but I think a linguist can explain the difference better than me by using correct terms.