you might want to mix up the grout then wait ten minutes, check how stiff it is , it should be quite firm like butter, dont worry just mix it up again dont add anything and you will find that it will soften enough to press into the joints.
Try a technique to wash off I have used for many years....once grouted, sponge over the tiles making sure to get the joints nice and full and evenly smoothed off. Dont be too fussy about getting all the grout off the tiles. then get another bucket of clean water rip a towel in half dip the towel into the water and just run it through your hands to get most of the water out. Then grab two corners and drape the towel onto the tiles and slowly walk back dragging the towel over the tiles. you might have to experiment a couple of times to get the right moisture content in the towel. When you have you will have a strip of very clean freshly grouted tiles the width of half a towel. Then repeat a few sq.metres at a time. This technique will cut your washing time by 2/3s and you will get a better finish than a sponge.
Just make sure the grout is quite firm in the joints before sponging and washing off.

Oh and the patches of light grout will have to be scratched out and grout the whole floor with the one batch of grout. Start the grout mix dry and firm and just add a little bit of water until its like toothpaste then wait and remix as per above.