newbie here

Hi. I am 27 y/o and am just now starting the <a href="https://glowing.com/glow-fertility-program">iui</a> process. I am not in a relationship and am wanting to become a smc. I have done all the thoughts and research about it and everything. I have already had my first vaginal ultrasound, lab work, and a hsg. Everything came back just fine. My thyroid hormone level was a little higher than my RE wants it so he's rechecking it in a week and a half. What's normally the next step. I am excited but I don't want to get too excited. I have only told 3 ppl of my plans and what I want to do. I'm normally an optimist but I can't help but continuing to think of what all could go wrong. I can't seem to get excited about it and think "this time next year my life could be completely different and I could have a little bundle of joy" but instead I keep thinking "what if it doesn't take?" Or "what if I miscarry?" I can't stop thinking of the negative things. Can anyone give me some advice about this?? 
Thanks everyone!!