There are a few different dialects which are spoken in China, so the way you say “I love you so much” will depend on which one you are speaking.
You say “Wǒ ài nǐ zhème duō” in Mandarin, or the more common Chinese dialect. When people speak about "the Chinese language", this is usually the one they are referring to.
Mandarin is the language spoken throughout the Northern and South Western areas of China.
If you want to say “I love you” in Cantonese, you would say “ngóh oi néih”.
Cantonese is another, very common language spoken in China, although it is more common in the South. This language is also spoken in Macau and Hong Kong.
The best way to learn a new language is to practice, so be sure to speak it as often as possible. Or if you get the chance, make the trip to China and make friends with native speakers.