I dropped my iPhone in water for 3 seconds

Hello,

You should rinse your iPhone quickly under tap water to clean it off, but besides that you should be good! iPhone 12 mini is water resistant. Learn more here: About splash, water, and dust resistance of iPhone 7 and later - Apple Support

From Apple:

1. If a liquid other than water splashes on your iPhone, rinse the affected area with tap water.
2. Wipe your iPhone off with a soft, lint-free cloth—for example, a lens cloth.

Make sure that your iPhone is dry before opening the SIM tray.

To dry your iPhone, tap it gently against your hand with the Lightning connector facing down to remove excess liquid. Leave your iPhone in a dry area with some airflow. Placing your iPhone in front of a fan blowing cool air directly into the Lightning connector might help the drying process.

Don't dry your iPhone using an external heat source or insert a foreign object, such as a cotton swab or a paper towel, into the Lightning connector.

Your iPhone can warn you if there's liquid in the Lightning port when you connect a Lightning cable or an accessory to your iPhone XS, iPhone XS Max, iPhone XR, or later. Learn what to do if you see a liquid-detection alert on your iPhone.

Thanks for reaching out!

-Drake

Very bad. Turn it off and don’t use it for several days. If you are lucky it may work when it dries out. If not see→Apple - Support - Service Answer Center

Adding more water and using water pressure is not wise. Just wiping it off is fine.