Hi Caley,
Can you post a pic of your top with the non-matching blocks? We might be able to help you figure out what happened.
Has anyone ever talked with you about "pressing" vs "ironing"? Ironing is dragging the iron over the fabric, which can lead to stretched bias and wavy blocks. Pressing is lifting the iron up and down, no dragging or swiping, and the blocks will not distort.
Regarding Connecting Threads, I have purchased kits from them before, they're actually a good place to start. CT is usually fairly generous with their fabrics, so if you make a small mistake it's not usually fatal.