Is this sentece punctauted correctly? i came home late; therefore, i didnt see aunt matildia

No, the sentence given:

"i came home late; therefore, i didnt see aunt matildia" — is NOT punctuated correctly.

The word: "didnt" should be replaced with: "didn't" (note the added "apostrophe")—or rewritten as two word: "did not". 

Furthermore, there should be a "period" at the end of the sentence.

As far as other grammar errors are concerned, the second instance of the use of the personal pronoun, "I"—is incorrectly written in the lower case: "i"—and should be replaced with the capital letter, "I". Furthermore, "aunt matildia" should be rewritten with a capital letter "A" replacing the word: "aunt" [the word: "aunt" should be changed to "Aunt"], and the name: "matildia" should be rewritten with a capital "M" replacing the name: "matildia" [the name "matildia" should be replaced with "Matildia"].  Also, if "Aunt Matildia" is, in fact, really spelled that way, than the spelling of the name should be retained.  On the other hand, if the aunt's name is actually spelled: "Mathilda"—or some variant, then the proper spelling should be used—and the first letter should be capitalized.

--Edit--- your question should read as follows: "Is this sentence punctuated correctly?"