A little too early to tell for sure, especially for a Muscovy egg. They take 35 days to hatch (versus other duck species who typically take around 28 days). Like maranfarmer suggested, I'd wait about a week and candle again. At that point you'll definitely be able to tell if any are developing.
Also, you should definitely mark down the day she started incubating (or as close as you can figure) and calculate 35 days from that so you know when to expect little ones.