To specifically answer your question, since it does in fact import as a square component, here's how I'd do it.
1. Import the bitmap, then use "Create a component from selected or imported bitmap" to create your component
2. Turn off the bitmap layer. You don't need it any more.
3. In the 2d view, select the component you created.
4. In the Drawing tab, click on the Trace Bitmap tool.
5. I chose the settings as shown in the following screen:
6. Select the vector you just created, and also select the component. On the Modeling tab, click on the "Clear area of selected model outside selected vectors" tool
You should be left with just the shape you want.
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