You shouldn't have any problems with that camera and flash.
Do not put it on manual unless you know exactly what you are doing. Flash, especially fill-flash, is requires a lot of extremely complex calculations, some guess work, skill, and good luck.
But auto-flash needs none of these things and the camera/flash just get on with it and do their thing very well. (You are set on auto flash?)
First thing to do is ensure you do not have any flash exposure compensation dialled in by accident. I am not familar with Nikon, but it shouldn't be hard to bottom that one out. Set everything to zero.
Fill-flash gives the most natural looking light, which means that the camera will adjust the shutter speed so that the ambient light is balanced with the flash light, which is adjusted by the lens f/number (and the flash power). Setting the camera to A (aperture priority) will usually engage this exposure mode automatically (it does with Canon) but just check the camera manual.
If the main subject is too bright, adjust the flash exposure compensation setting to -1 or -2. If the background is too dark, adjust the camera's main exposure compensation setting to +1 or +2. By using those two coontrols you should get a good result, and can then fine-tune it to get the kind of result you want, but I would be surprised if you don't end up with both settings close to zero/neutral balance.
There is a danger that you are too close with the flash. This can give white-out faces and also very dark backgrounds as the flash light falls off very quickly behind the main subject. But fill-flash should sort that for you, maybe just move back a bit to make sure you are within range of the camera/flash adjustment. If you have the ISO cranked up to 1600 or something very high, this could be your problem.
