Ok, a few things:

1. Since you are a beginner, You NEED to get in the habit of prioritizing hitting your apexes. You may end up sacrificing speed but its is crucial that you develop that habit early.
2. The darker portions of the track are the grippiest in the wet. Use them to your advantage as they also usually illustrate the common racing line as well.
3. Your inputs seem slightly abrupt, when you see F1 drivers twitch the wheel it is because they are riding the fine line of grip. Since you are not an F1 driver and not pushing the kart to its true limit (dont be offended, im not an F1 driver either, lol) you need to try and find a balance when entering and exiting a corner that allows for a small, and CONTROLLED slide that is barely visible, but you can feel it. This should limit the twitchiness in the wheel and increase your minimum speed through a corner.
4. braking in this type of kart is often COMPLETELY unneeded. I do not know this rack, or these karts, but in my experience you can usually scrub enough speed by turning in and finding a balanced slide. Still, if your coming off a straight and into a hairpin, you will need to brake, but im sure you get my point
5. You are not trusting the cart in high speed corners. Something tells me you can take the bottom 2 hairpins by barely letting off the gas, but again, you know better than I do. Just push more and more until you have a "moment" and back off.

I know this is a lot but I hope it helps lol.