HI Coffee lovers around the world !

I have just started working as a barista and everything is going really well except I need to understand about adjusting grinder and dosing a lil more, so I was hoping someone could clarify and explain

My shop has the following recipe:

dry weight = 20.8-21.2g ( double shot)
extraction = 28-32 second

Today, my shot ran at 25 seconds. I used the scale to weigh my shot's dry weight in a group handle, which was 19.2g. So both , extraction time and dosing was short and way off.

So, I adjusted the grinder to make it finer, which made the extraction time to be 34 seconds. I weighted the shot again which changed in weight and was now 19.8 grams.

Now I understand that you grind finer to make extraction longer , and coarser to make it shorter. But what about dry weight of the shot ? I heard , that I could actually change the weight of the shot by making it finer/coarser. And that I shouldnt really touch the dosing setting. Is this true ? if yes, I d like to understand how the weight of the shot is affected by how you adjust fine/coarse grind. PLS also help me figure out, what I should've done if the weight of the shot was 1 gram short of the recipe.

Thank you all in advance ! sry if this question seems a bit silly