Question

how did the civilization get the name harappa

Answer 1

Harrapan is the name of one of the major settlement in there Indus Civilization, it usually isn't cakled Harrapan civilization. Mohenjo-Daro was aslso one of the major settlement in the Indys Civilization.
The origins of calling it Harrapan Civilization probably lie in textbook which have created the Democratic -Republican Party which is a confusing name.