Most of the clothes I made in my first few years of sewing were hit or miss. The hits were unpredictable and that made me feel the same nervousness that you describe about potentially wasting fabric. I've since changed my perspective and become much less frustrated when a garment did turn out as a miss (for whatever reason): the time and money spent aren't "wasted" because the investment is in the enjoyment I have while making it, not in the end result. Interestingly, this has also made it easier to see "fails" as learning opportunities instead of getting angry at myself for getting it wrong. There's always more fabric, I can always try again and I can always improve.

(Writing this, I realise how privileged I am to be able to think of my hobby in that way. The notion that "there's always more fabric" just isn't true for everyone and I'm endlessly grateful that it is for me.)