http://quiltinaday.com/theater/qbab/qbab12.html
Here's a link to one of Eleanor Burn's teaching videos that shows how to do that center swirl that really helps distribute the bulk in the center of a block. Also, press your other seams so they "lock" into each other as much as possible, that way you don't have seams piled on top of each other. As for your half-square triangles, I think the puckers will quilt out.
Your quilt block is beautiful. Don't be too hard on yourself and enjoy making a beautiful quilt!