The is how the Spitfire flies. You need to do 3 things to correct it.
First, using the manual, make sure you have your RPM & Boost set for proper Cruise settings. Going from memory, I think 2100 and +4 works for most situations.
Next, use the rudder trim to center up the slip indicator.
Finally, open the handy tablet and go to the far- right tab, which I think is options. There, you will have the little cheater Aileron trim, which does not exist in the real plane. They’ve put that there for your convenience if you don’t want to hand-fly it as much.
Keep in mind, this is a very well simulated plane. These settings will not be a set-it-and-forget-it situation. As you burn fuel, and your plane gets lighter, you’ll need to adjust. As weather conditions change, you’ll need to adjust. Same for altitude changes, pressure changes, and who knows what else.