The gauge tries to stretch itself into the given space. If you put the gauge in a Grid, the gauge should stretch as much as possible within this grid. However, if you put the gauge inside a stack layout, then it will try to shrink to as little as possible, because of how the stack layout works. So, if in your case the gauge resides in an element that lets the gauge choose its size, the gauge will choose a small size.
If you are using the Beta, you must know that we had not yet taken into consideration the difference between the device true pixels which the SkiaSharp works with and the device independent pixels XamarinForms work with. So, if you are using the Beta, issues like unexpected sizing are, well, expected. You can upgrade to the last official version in which this was addressed.
Let us know if you need further assistance.
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