It's "I studied math in college,"

NOT "I studied maths in college."

'Mathematics' is used with a singular verb.

'Mathematics' is a mass noun.

"The mathematics of quantum physics is complicated" is CORRECT.

"The mathematics of quantum physics are complicated" is INCORRECT.

"Mathematics is used throughout the world as an essential tool in many fields" is from Wikipedia.

You can substitute 'math' for 'mathematics' in each sentence in American English. Try that with 'maths'.

Math is fun.

Maths is fun?

That's hard to say. :)

'Maths' should be taken with a grain of 'salt' — another mass noun!