I'll help as best I can, sure.
Different colleges teach different modules I expect, but they would largely be the same and engineering-related. Mine was focused on maths, mechanical science and electrical science. Maths is what you would expect - algebra, trig, basic calculus, statistics, exponents, logs, probability, fractions etc. Mechanical science was more focused on physics and report writing. Linear motion (think gravity, velocity, acceleration etc), statics (loads on a truss, stress/strain). We had to write a few reports on things such as power transmission (gears, clutches, linkages and so on) and material properties (do experiments on the heat capacity/strengths of copper/aluminium/steel, compare and analyse the results, that kind of stuff). Electrical was all about circuit analysis, voltage/current/resistance/capacitance/magnetism and so on.
There were a few other things too like English (which I had to do because my GCSE had expired) and study skills. Study skills was basic stuff like making timetables, CV's, with some more report writing to introduce us to proper referencing systems and that kinda thing. There was also a presentation that I was worrying about all year but ended up being super-easy and not nerve-wracking in the slightest. Ok, maybe just a little bit.
45 credits at level 3 with 30 at distinction seems to be the normal requirement, but different universities want different marks. It's also important to consider that some universities will require you to complete a foundation year if you've done an Access course, whereas others will accept you straight into year 1 of the degree program. The foundation year is considered a 'year 0' and for most universities it's integrated into the degree program. Basically, you will be doing what you did in the Access course again but in much more detail. I purposefully went for the universities that offered the foundation year because I think that going over what I've learned again will really give me a solid base for year 1 of the degree, and judging by the modules I'll be doing there is a helluva lot of stuff that the Access course skipped over. Other people don't want to spend another year redoing the same material so they go for universities that will accept them into year 1. That's a choice you will have to make.
In the end I had to make a decision between two universities - Swansea University and University of Sheffield. Both foundation years. Sheffield wanted 30 distinctions and 15 merits, Swansea only wanted me to pass the Access course (literally just pass, no distinctions or merits). Even though at the time Sheffield was (still is) ranked higher for engineering (it was 3rd whereas Swansea was 20-something) I went for Swansea due to a couple of reasons - I visited both on open days and simply got a better feeling from Swansea. Also, they offered me a £3000 scholarship which Sheffield didn't. I needed to get 33 distinctions and 15 merits for the scholarship and I ended up getting 48 distinctions so I more than achieved that, and now I can look forward to a nice extra £3000 to spend how I see fit. The other reason is because they're building a brand new £450m campus for engineering which opens next year, so it seemed like a good time to get in because I can only see the university improving. The course I'm starting in September is called BEng mechanical engineering with a foundation year. I do have the option to change to a MEng given I do well enough by the 2nd year (3rd including the foundation year) and I have the option to do the year in industry too which I fully intend to, again only if I achieve a respectable mark (60% I believe) by year 2.
I am in no way super smart. I'm a completely average guy and before the course started I was absolutely terrible at maths. I hadn't used it for 9 years and I had forgotten everything. I couldn't divide.
So I worked my ass off, and made sure I did every assignment as well as I could. I also made a couple of friends which was incredibly helpful because we'd help each other out (not by giving each other the answers, you're just cheating yourself. We'd all complete the assignments by ourselves and afterwards we would compare. 90% of the time we would have the same answers but on occasion one of us would have a different answer so we'd all work through the problem together to see what happened). Of course, that was only helpful for maths and the like. For the reports we were totally on our own. YouTube was an enormous help too, there's so much out there that can help you.
Work hard, make sure your answers are correct, get your assignments in on time and you will get distinctions. It's extremely doable.