That's actually pretty f@cking good for a first try!!!! To me it looks like the tiny gap is the width of the pencil mark. Perhaps scribing the second cuts using a knife or a chisel would get you to the precision you seem to want.
You can use sawdust and glue to make up some wood filler and seal that right up. Even the pros do it.
That's also very thick wood for a dovetail. I'm a little lazy with respect to woodwork, so I'd recommend a simpler joint that provides similar structure
Haha I actually did use a knife to scribe a dent to place the saw at to help me start the cuts but I just suck at sawing 😂 And yes I will use a thinner wood next time, this was just because it was the only piece I could easily get square to start with. The miter saw we have on loan has the shittiest blade so I couldn’t cut up a thinner board to use. I’d definitely do some patching up if I were to use this for something but this is just a practise piece and I want to just leave it as is to look back on if I ever get better 😂
I think you are rocking this!!!
I'm going to assume that your technique for sawing is perfect. 😀 But saw's are always rough. So, saw further inside your line - maybe 1mm. Then use the chisel for finishing the cut.
I'm still amazed you got it that good on the first round. Treat that as a success!!
You should have seen me, I tried everything in my power and kept changing between chisel, saw, knife and box cutter to try and get even lines 😂
I've been there. I feel your pain/sorrow/frustration.
Soon enough, you'll be making some of these.