If you fail/get pulled, you will go into remediation swim where they will teach you what you need to know to pass the main course. However, you don't want to go to remediation. The instructors are great and super encouraging, however, it's a pain in the butt and it can be avoided with the amount of time you have.
Strokes: freestyle, breaststroke, side stroke and jellyfish backstroke. If you can do these, you'll be fine.
There are two events people struggle with in air water survival (AWS). However, if you really suck, they'll pull you before you even get the chance to fail at one of these. On the first day, they'll have you do some basic strokes, and if you are a risk to your own life, straight to remediation swim. If you make it past the basic strokes, your only real remaining obstacles are these two events: the tread and floats and the tower to line.
Tread and floats: Swim in place (tread) for 2 minutes then deadman float on your front (NOT ON YOUR BACK) for 7 minutes. You'll start in just a swimsuit and you'll progressively add weight until you're in a full flight suit, boots and gear. This is the number #1 thing that people struggle with. People float naturally. Many people who went through remediation claimed they don't float, we had them hold their breath and *magic*, they floated. I can think of 2 individuals out of 100+ people who went through remediation who, despite holding their breath, sunk a little. These men were built like trucks and had 0% body fat on them. They were still able to pass the tread and float with some coaching. The key to the tread and float is to remain calm, hold your breath (to float) and frog kick. In those boots, you will sink like a stone if you try to flutter kick. You will be tired and struggle to stay up after 2 minutes, that's the idea. You need to slow your breathing, take a big breath and chill out to get your heart rate down during the float. You should be bored after a couple of minutes, not panicking for the full exercise. I would recommend getting an old pair of boots + some old clothes and hop in the pool.
Tower to line: You jump off a tower and swim to a mark on the bottom of the pool. I do not know the exact height or distance. Estimates are the tower is 15ft and the distance is 19m. The pool is 25m long, and the mark is around the 3/4 length. While the tread and float is what people struggled with the most, the tower to line is what I saw attrite the most people. Attrition due to AWS is very rare, however, people suffer from a fear of heights that can be extremely challenging to mentally overcome. Tread and floats you have coaching and lifeguards right next to you. Tower to line is you versus that pool, underwater. Just like the tread and floats, you progressively work up from a swimsuit to flight suit and boots. You do not wear extra gear for the tower to line, so do not worry about extra weight. I have a crummy lung capacity, so I personally had a hard time with this. The key to the tower to line is, again, to remain calm. When you put boots on, again, the flutter kick will get you nowhere. You have to frog kick and pull with your arm. To practice this, I would recommend either finding a pool with a high up diving board to jump off of or giving yourself a big push against the wall and then practice holding your breath to make it to that 3/4 mark on the pool. Make sure to jump with the abandon ship position. You can also give yourself some horizontal distance via a "super Mario jump" as to not have to hold your breath as long.
You mentioned being nervous for the mile. Don't. I saw a single person fail the mile, and its because he suffered from a severe cramp and got himself out of the pool. Some get close to the max time but no one ever went over.
Also, helo dunker is a cake walk. If you can pass AWS, you'll pass the helo dunker.
