(2) is incomplete and doesn't sound right. (1) probably makes sense, but the simplest and most standard way of saying this would be:
私が悪い点を取ったのは、勉強しなかったからです。The reason I got a bad grade is that I didn't study.
The underlying grammatical form here is 「〜のは〜からです」. You can see more on that in this answer, which gives the following example:
お菓子を食べたのは、おなかがすいていたからです。The reason I ate snacks is because I was hungry.
ということです is one of those quite versatile and enigmatic phrases in Japanese that is hard to pin down when trying to dissect the parts of a sentence. My impression is that it's often used just due to the speaker's force of habit without any real effect on meaning. When translating from Japanese into English, there will often be no equivalent of it in the English translation—i.e. it is often valid to translate the sentence as if it were not there.
As a learner, if you are looking to be understood it's probably simplest to stick to standard forms like 「〜のは〜からです」 for your own writing/speech, and learn from examples like this that there are always often ways of saying the same things in Japanese. 「ということ」 is a useful phrase to throw in here and there but getting an instinct for when it can be used comes with time.