Neither of them in American English. "I got full marks" or " I got one hundred marks" sounds like it may be British English. I would say, "I got 100 percent on my exam."

No 1 is better as it indicates 100 % in the exam. No 2 is ambigious because the reader doesn't know how many marks the exam consisted of.

#1 works well in American English, except that we use the preoposition "on" when referring to an exam/assessment. For example, "He missed the last question on the test" or "I got a 100 on the exam." I also recommend the phrase "I aced the test!", which is synonymous with "I did very well on the test!"

The 1st one

Neither. Please remember, the USA is not a monolith when it comes to language. Each region/state has a different type of vernacular. I would state, in this case: "I made a hundred!" or "I made an A!"