Failed batched?

To be honest I think it had failed before it even started as I made the mistake of boiling the apples to get them soft enough to squeeze the juice out, ended up with a very thick and syrupy liquid, which i had to water down with water and shop apple juice... So I never expected the highest quality cider but anyway, it bubbled quite a lot at first and smelled a bit like eggs when I opened it to smell, then seemed to go quiet around the 7th or 8th day and the smell got a little better, but still kinda eggy. I left it another 5 days and didnt have any more bubbles so I figured it was done.

So I just filtered it through a very fine sieve and threw away the last 20% which was all sludge. But it still smells a little bit rotten, just a bit... Tasted it and it wasnt completely gross but a little sour, like wine that had been opened and left for a few days.

Any idea what this means and is there any way to save it? I bottled it anyway as I thought it might get better after a few weeks sitting. If it is undrinkable, could I still use it for applejack?

What is the exact recipe and steps used do you know sg and Fg?

First of all what are SG and FG? Im guessing gravity? I'm a complete newbie and dont have any equipment so couldnt check it.

The way I made it was from 3.5kg apples which I cooked and squeezed 2litres of juice from, 1 litre apple juice, maybe half a litre of water, 1 cup of sugar, and 2g bread yeast and after a few days I boiled a few raisins and added the water from that after someone suggested it to me. I made it on 2nd of feb and it sat since then in the corner wrapped with blankets, room temperature was around 50-65F so a little cold.

Like I said it doesnt smell absolutely horrid, but it definitely doesnt smell good, and the taste is a bit sour, I didnt spit it out but its not something I really want to drink either. Oh it tasted a little sweet also, was expected it to be completely dry, so the fermentation might have stalled because of the temperatures.