You are doing the right thing. You have upped the lessons, doing private practice, put the test back until ready. These are all absolutely good things. I think one of the main things is to put things in perspective. Yes, you are not yet ready and still struggling, but think back to when you started and all of the progress and good things you have achieved. It's very easy to just focus on the negative. Also let's put 48 hours in to perspective. 48 hours of driving experience is really nothing at all in the grand scheme of driving.
Put 30 young pupils in a classroom for a lesson. By the end of the lesson, not all pupils attain the same level of understanding or grasp the concept equally. Just because it takes you longer to grasp that concept does not mean that, in the end, you don't have the potential exceed the understanding of the concept. You may even eventually, grasp it to a greater level. Take a race, a sprint racer will pass the line quicker than a marathon runner, but learning the skill of driving is not a sprint race, it's a skill you learn for life. You have to be bad, struggle and fail at something, before you get good.