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Just keep going and be patient! You will overcome such issues soon if you practice consistently.
You may try to fix your string muting by going over each finger individually, adjusting its position slightly until you get the strings affected by it to ring out clearly.
One thing that helped me a lot was to keep the nails of my fretting hand as short as possible as this opens a wider range of positions and angles.
Also try to adjust the force with which you press the string down. We, as beginners, often tend to push the string harder than necessary.
Don’t worry too much and don’t get discouraged! We all may strum a thousands songs on such and similar issues that all of a sudden play no further role in our playing, by just practicing and enjoying each single note we produce on that beautiful instrument!
Cheers
Markus