Don’t worry about it (though I curse the scales on almost a daily basis)
300g is a cup of coffee by weight, and your body can be carrying an extra 1.2+ kilos of fluid at any time, not to mention the solids.
Good nutrition, a slight calorie deficit and some exercise will have the right effect long term - look at your weight chart in a couple of months and you won’t be able to see this little blip.