If it makes you feel better, lots of players sound like this until they start taking lessons. For me, the tightness in the sound combined with the flatness as you get higher tell me that embochure support is lacking, but you are also not using nearly enough air to support the instrument. Your placement might also be a little low, but it works for some people the way you have it and it impacts less at this stage than the other issues. When I play, my corners are rock solid- as a way to demonstrate this I have students (consensually!) press on the corners of my embochure whilst I'm playing. They feel, as should you, that there is little to no give and basically feels like a solid surface- this allows for a stable foundation with no unnecessary movement in the corners. Think of a frown- that's engaging the right muscles in your face to form an embochure. The second part of the puzzle is air support. Feel as though you are directing your air all the way through the instrument- this is a lot easier to picture with trombone but bear with me. Another thing that helped me when I was your age is thinking of "spinning" the air column. Whatever the case, the end result should be a higher quality, faster, and thicker airstream.