Hiya Col,
The quote you get is just an indication as our price feed is atl least 15 min delayed, and hence you have to wait 15 mins for it to get actioned, so that it's near-realtime (its the best we can do until we get a realtime feed). So very often the price you get can actually improve or unfortunately in your case, worsen 🙁
Cheers
Sharky.