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You're approaching the job wrong. Think of the shape you want, and sketch it. It looks like maybe you're thinking like a machinist - cut the shape you want from a stock shape. There are times to work like that, but you need to learn to just make the shape.
I recreated your part from your sketches mostly. In the screen capture you can see all of the sketches. If you can get your hands on the commercial training books, one of the first lessons has a great example of what sketches you can use to create different types of shapes. You really need to go through that. It shows a feature, and 3 different sketches you can use to create it, and which one is the best and why.
You also still need to work on sketch relations and dimensions. Tangent arcs in particular seem to be a problem.
Are you working with a teacher or using a book of some kind?
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