If you think you have found the right jewellery shop/online site on the first look, keep looking anyway. You can compare quality and pricing and then make your decision from there. You don’t need to feel pressurised to spend days or weeks looking; a few hours one morning or afternoon can often be enough.
Once you have chosen the place to get the ring, do feel free to ask questions before buying.
Go in store, send an email or call the company. Ask about the 4 C’s of an engagement ring (Carat, Clarity, Colour and Cut) and take notes if necessary. And don’t be afraid to ask to see more than a handful of rings if you are in store.