Well, you are definitely a determined piecer, Sunny Days, and I applaud any and all efforts find a way to get it done!
I hope you'll try another one using the partial seam method so that you will have that trick in your bag for the future. As for the triangles that came out just a bit too small for the pattern as planned, you'll get that down too with a bit of practice...I'm guessing that they are off by just a little over .5"...most newer directions use a square in the corner sewn on the diagonal to create that "snowball" corner...this has a cut triangle so you would lay it right sides together with the rectangle and sew along the long edge of the triangle using a scant 1/4" seam allowance...then press it carefully back over the rectangle...for stability you can leave the rectangle intact...that also improves accuracy as the rectangle will remain true to size. Hey, I'm proud of you for stayin' with it...you've got lots going for you...stay with it...piecing takes practice but you're waaaaay ahead of the curve! Happy stitchin' to ya!