“There is no one worthy of worship except Allah (God) and Mohamed is the final Apostle (messenger/prophet) of God.”
One not only has to say these words but should also believe in this testimony of faith to be a Muslim.
Having a Muslim name, living in a Muslim country, having Muslim parents cannot make anyone a Muslim. It is the fundamentals and principles that you follow which can determine whether you are indeed a Muslim or not. You cannot be judged by your words but only and only by your actions.
Apart from the religious obligations, the 5 pillars of Islam, we as Muslims also need to have the Islamic character within ourselves. Quran, the last words God, remains unaltered and the life and living of Mohamed (peace be upon him), which can be learned from his Sunnah are the fundamentals of Islam, therefore it is the belief and practice of every Muslim. The teaching of Islam tells us the important characteristics of a Muslim.