No! It is not enough to be a Catholic to get to Heaven. One has to be a good Catholic. "Many Catholics will be lost, because they are only nominal, not practical, Catholics, and because they reject some doctrines of the Catholic Church, especially such as oppose their inclinations and passions. Remember, he who rejects even one doctrine proposed to our Faith by the Church will certainly be lost (James 2:10), even though he should lead a good life." (From THE PULPIT ORATOR, Volume VI.)
Our Lord said, "He who believes shall be saved" (Mark 16:16)~ But God said many other things as well:
"If you love me, keep my commandments" (John 14:15); and "If thou wilt enter into life, keep the commandments" (Matt. 19:17).
"He that blasphemeth the name of the Lord, dying let him die" (Lev. 24:16).
"Keep you my Sabbath: for it is holy unto you. He that shall profane it, shall be put to death. Everyone that shall do any work on this day shall die" (Exodus 3l:1-15).
"Know you not that the unjust shall not possess the kingdom of God? Do not err: neither idolaters, nor thieves, nor covetous, nor drunkards, nor railers, nor extortioners, shall possess the kingdom of God" (1 Cor. 6:9-10).
"A thief is better than a man that is always lying: but both of them shall inherit destruction" (Ecclus. 20:27).
"Neither fornicators nor adulterers . . . shall possess the kingdom of God" (1 Cor. 6:9). "You have heard that it was said to the Ancients, 'Thou shalt not commit adultery.' But I say to you that anyone who so much as looks with lust at a woman has already committed adultery with her in his heart." (Matt. 5:27-28). "Keep thyself chaste" (1 Tim. 5:22). "Blessed are the clean of heart for they shall see God" (Matt. 5:8).
"There is not a more wicked thing than to love money, for such a one setteth even his own soul at stake."(Ecclus. 10:10).
"If anyone lie with a man as with a woman, both have committed an abomination. Let them be put to death" (Lev. 20:13).
"Hear me, and I will show thee who they are, over whom the devil can prevail. For they who in such manner receive matrimony, as to shut out God from themselves, and from their mind, and to give themselves to their lust, as the horse and mule, which have not understanding, over them the devil has power" (Book of Tobias, 6:1&22).
And Christ's Mystical Body on earth, His Church ("He who hears you, hears Me" - Luke 10:16), says:
"Each act of marriage must be left open to conception" (Pope Pius Xl's Encyclical "Casti Connubi", December 31, 1930).
"If anyone says that the commandments of God are, even for one that is justified and constituted in grace, impossible to observe, let him be anathema" (Council of Trent, Canon 18 on Justification).
"If anyone says that a man who is justified and however perfect is not bound to observe the commandments of God and the Church, but only to believe, as though the Gospel were a bare and absolute promise of eternal life without the condition of obeying the commandments, let him be anathema" (Council of Trent, Canon 20 on Justification).
Therefore, although it is true that Catholics alone profess the true faith "without which," as St. Paul assures us, "it is impossible to please God" (Heb. 11:6); nevertheless, as St. James concludes: "Faith, without good works, is dead" (James 1:22:27).
"Sometimes people say 'It is better to be a good Protestant than a bad Catholic.' That is not true. That would mean at bottom that one could be saved without the true Faith. No, a bad Catholic remains a child of the family - although a prodigal; and however great a sinner he may be, he still has the right to mercy. Through his faith, a bad Catholic is nearer to God than a Protestant is, for he is a member of the household, whereas the Protestant is not. And how hard it is to make him become one!" (St. Peter Julian Eymard, 1811-1868).
Source: Open Letter to Non-Catholics