Don't stress
I'm in the same boat. I haven't started yet because I haven't been able to afford the revision books until now (I'm getting the Heywood book next week). Though I have been reading/watching some related stuff without making notes, because I became interested in it (I didn't do it for revision purposes, but I guess what I've been looking into has been useful); stuff such as Christopher Hitchens talking about socialism, or Noam Chomsky, or reading a book that I borrowed from the library called "Conservatism" by Kieron O'hara.
But I'm also resitting my Philosophy exam, and haven't revised for that either D: Next week I'll be getting all the books I need and really getting down and doing some proper revision. I think I'll be fine as long as I do an hour or two every day (and I'll probably end up doing more most of the time, because when I start revising I usually start enjoying it).
I don't think it's too late
There's a lot of wriggle room in the ideologies exams so it's not as if you should feel like you have to learn absolutely every little piece of information. I mean I'd say you could probably know the basic philosophies and key concepts of an ideology within a few days. It would only take a few days to, for example, learn about how conservatism is mainly concerned with change, is reactionary, is sceptical both epistemologically and about human nature, is paternalistic, likes traditionalism etc. etc. So really, for three ideologies that's three weeks to get to grips with the basics, and from there-on you just fill your head with as much as possible relating to the ideologies, in terms of quotes and history and contemporary policies.
What I've also started to do is to read the newspaper, and keep a note-book next to me, where if I spot anything that could relate to an ideology, I write it down in the notebook and how it relates to the ideology. For example in a newspaper, it was mentioned that Ed Miliband used the term "one nation" a lot in his 2012 Labour Party Conference speech, and I immediately remembered that that was a conservative term, mostly used by the conservatives of the post-war era (i.e. "one-nation conservatives", those whom Thatcher called "the wets"). So I now have mental ammunition for the argument that modern Labour is not what it once was (i.e. attempting some form of socialism), in the same way that many argue that Labour have been conservative from the time that Blair came into power.
So looking into the news is a helpful thing to do, too. It's especially good because it shows the examiner that you're able to make connections outside of the course, and are not just regurgitating text from a textbook.
I don't think it's too late if you have the time to revise every day