I have a couple questions about Hargreaves Lansdown

I have put money into a legal & general top UK 100 index fund because I've been advised that it's a good idea, but after like 4 months it's only gone downhill. Should I take the money out and switch it to another stock or should I keep my faith in it?

Another question, when I click on a specific stock and look at the time period graph, it never makes any sense. For example, I'll click on the past month graph and it will be mainly blue (in the positive) for example its saying that on the 31st July, the stock was positive. But when I click on the 3 months graph, it says the stock was negative at the same date, wtf? Can anyone explain?

Thanks