How many grams of espresso are coming out at the other end? The rule of thumb is around 2x the mass of coffee in the portafilter. However, that's just a rough guide. Generally, more water -> more extraction -> less sour. Just for experimentation's sake, try adjusting variables like fineness or water, and let the shot time go longer. See how you like the results.
I tried to follow all the rules of espresso. "Only X seconds of brew time", "Only this Y grams of water". I never got a good tasting shot. Then I started experimenting. I have a pretty cheap DeLonghi Dedica, and I began to tailor my shots to how my machine actually works, vs how others told me to do it.
Nowadays, I pull a ~43g shot from 18g of coffee. I have my grinder set to some fineness level that I haven't needed to adjust in months. The shots I pull are always better than most non-specialty coffee shops. Sometimes, I even get a perfect shot that tastes like heaven. It all became better when I stopped focusing on rules and started learning what my machine likes.