Not being critical here, just offering some advice on what I think could be your issues. Feather3 did give you some excellent advice.
It appears to me you may have both cutting and piecing issues. If you are using different rulers for different purposes - for example a large one for general cutting and a smaller one for trimming - try to make sure all of your rulers are of the same brand. Not all rulers measure the same! For me, it helps me to be consistent with cutting if I put a sticky note or piece of tape on my ruler when cutting mutliples of the same size. Otherwise sometimes you place your ruler on this side or the other side of the line - at least I do!
Not sure if your seam allowance is consistent. Again, sticky notes or tape are your friend. I tried one of the seam guide 1/4" feet for my machine and found that the seam allowance was greater than 1/4". My machine has a 'scant' 1/4" position so that is what I use. If I manage to keep my fabric lined up with the edge of the foot, my seams are a 'scant' 1/4" all the way along.
I also press my seams open vs to the side. I feel it gives me an overall flatter block but I also feel it makes it more accurate for me to match seams/points. When doing this, I place a pin straight down through the top pieces I'm matching up and then take the bottom section I'm matching and place the pin straight down through that piece. Hold the pin straight up/down while lining up that intersection top/bottom. Once the pin is straight and the top/bottom pieces match, I place pins on either side as close as possible to the straight one. Remove the straight up/down one and then sew. I then pin the balance of the section, matching the ends of the section. If there is a bit of a discrepancy between those two edges, I will 'ease' the larger piece/stretch to smaller piece while sewing ever so slightly. I try to do the 'baggy on the bottom' theory but that's not always possible either.
Press your units thoroughly after they are constructed. Measure to see if they are the size they are supposed to be. Trim if necessary. But don't trim off your points! It's a very tedious process but I press each seam after it's sewn to kind of 'set' the thread into the fabric. Then press my units open they way they supposed to be. That is when I measure/trim if needed.
You're doing a great job. That's a pretty complicated block for a beginner but I also believe in making things you like regardless of how 'difficult' something is rated compared to what you think your skill level. One of my first quilts was a Leymone Star made with strip sets. Much repositioning of the ruler and trimming while getting that 60 degree angle and lots of pinning. It turned out great! Only a table topper but a great piece nonetheless. No one told me it was supposed to be difficult, lol.
'Press' on!