Thanks for the pictures and description. Your block looks beautiful. You will always remember the challenge and be happy that you mastered a new technique.
Here is a how to video for you.
https://www.youtube.com/watch?v=Z2ywLp-sBKg
What ruler are you using to square up the HST? Check to be sure the 45 degree line going through the center diagonally is on the seam line. Then you measure out the block and cut the extra fabric.
In this one, you can see how to trim the sides, turn, and trim the other sides.
https://www.youtube.com/watch?v=5I-U_ZYcXH8
Hang in there and you will be fine!