Was the soup watery or thick?
If it was watery then it can seep deeper inside, which will need you to open the system up quite deeply to get to the spillage. At that point I would recommend you speak to your parent on getting the system in to someone who has the tools and skills to work on your system.
If the soup was on the thicker side then you maybe able to pop the key caps off and clean the spill up from just under the caps as the soup wouldn't have traveled as far. This is something you can do just take your time and be careful as you can break or loose pieces here.
Here's a good YouTube vid on popping them: Removing the key caps on a Macbook Air 2011/2012 the correct way. Once you get the cap off you can also remove the scissor mechanism as well. Then with a cotton swab (Q-Tip) slightly moistened with distilled water carefully wipe down the area underneath. You can stick the caps and scissors into a cup of distilled water to clean them and using a soft toothbrush scrub anything that is sticking on them. It will take quite a few swabs to clean things up. The trick here is not to get the system overly wet as you don't want the water to drip into the system only wet enough to get the soup out. You really need to use distilled water as your tap water has minerals in it which can cause problems when it dries unlike distilled water.
Some the bigger keys have a wire torsion bar which needs to be correctly inserted so when you pop the key cap note how it goes back.
Hopefully that will take care of it. If not you'll need to get the system serviced and depending on what they find they may need to replace the entire top case. - Good Luck!