You are misreading the hydrometer. If the coopers kits says the OG is 1.040 and you added the correct amount of water and sugar[~] then your OG *was* 1.040. So that's that.
So you have two weeks to practice reading the hydrometer. 0.990 is impossible because a reading of less than 1.000 means the wort is *less* dense than water and as sugar makes liquids *heavier*, only alcohol makes liquids lighter. And you didn't start with any alcohol.
Take a measure with just water. That should be 1.000.
Try mixing one oz (in weight) of table sugar into one cup of water. (Stir well to make sure it dissolves). That should read 1.046[*].
If your hydrometer is consistently off then your hydrometer is poorly calibrated (it happens) and you'll need to adjust your reading. Otherwise try to notice if you hydrometer is sticking to the side of the sample jar. Try spinning the hydrometer. Many people say they take samples in the tube the hydrometer came in, but I have found I've never been able to as it is too narrow for the hydrometer bulb to float freely.
Some hydrometers come with multiple scales. Perhaps you are reading a wrong scale.
Hopefully we'll get it figured out in the next two weeks.
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[~] I actually don't know whether the Coopers kit required sugar. Some do and some don't. If it didn't don't worry. In either case, if we assume you added the right amount of sugar and/or water your o.g. should be set in stone.
[*] FWIW Rule of thumb: one pound of sugar in a gallon of water has a reading of 1.046 or has 46 gravity points. (A gravity point is to subtract the 1 and multiply by 1000). We say sugar has 46 points/pound/gallon or 46 PPG. A PPG means a substance (a sugar, a grain, an extract, etc.) has enough sugar so that one pound of the substance in a gallon of water will raise the specific gravity by 1 point. This is very useful in calculating your brews and measurements.
Your coopers kit has a specific PPG and so by adding it to the correct amount of water (and sugar, if nesc.) we *know* your OG had to be 1.040 (assuming we trust what Coopers told us).
As a cup is 1/16 of a gallon and an oz (weight) is 1/16 of pound. We know one cup of water mixed with one oz. of sugar will also have a specific gravity of 1.046.