Yes, Jehovah’s Witnesses are under a curse because their trust/confidence is in men who have them "working hard for the reward of eternal life" while salvation and its benefits are actually gifts of God’s grace.
Salvation And Its Benefits Are Gifts Of God
SALVATION A GIFT
Ephesians 2:8 For by grace are ye saved through faith; and that not of yourselves: it is the gift of God. 9 Not of works, lest any man should boast.
JUSTIFICATION A GIFT
Romans 3:22b-25a… for there is no distinction; 23 for all have sinned and fall short of the glory of God, 24 being justified as a gift by His grace through the redemption which is in Christ Jesus; 25 whom God displayed publicly as a propitiation in His blood through faith.
Roman's 5:18 Therefore by the offense of one judgment cam upon all men to condemnation; even so by the righteousness of one the free gift came upon all men unto justification of life.
ADOPTIVE SONSHIP A GIFT
John_1:12 But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name:
Romans 8:15-17 15 For ye have not received the spirit of bondage again to fear; but ye have received the Spirit of adoption, whereby we cry, Abba, Father. 16 The Spirit itself beareth witness with our spirit, that we are the children of God: 17 And if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together. (also Galatians 3:26)
Galatians 4:4-6 4 But when the fullness of the time was come, God sent forth his Son, made of a woman, made under the law, 5 To redeem them that were under the law, that we might receive the adoption of sons. 6 And because ye are sons, God hath sent forth the Spirit of his Son into your hearts, crying, Abba, Father.
ETERNAL LIFE A GIFT
Romans 6:23 For the wages of sin is death, but the gift of God is eternal life through Jesus Christ our Lord.
1John_5:11 And this is the record, that God hath given to us eternal life, and this life is in his Son.
John 17:3 "This is eternal life, that they may know You, the only true God, and Jesus Christ whom You have sent.
FORGIVENESS A GIFT
Romans_5:18 And not as through one that sinned, so is the gift: for the judgment came of one unto condemnation, but the free gift came of many trespasses unto justification.
Ephesians 1:7 “In Him we have redemption through His blood, the forgiveness of our trespasses, according to the riches of His grace.”
Eph. 4:32 And be ye kind one to another, tenderhearted, forgiving one another, even as God for Christ's sake hath forgiven you.
RIGHTEOUSNESS A GIFT
Romans 5:17 For if by one man's offense death reigned by one; much more they which receive abundance of grace and of the gift of righteousness shall reign in life by one, Jesus Christ.
Romans 4:23-25 Now it was not written for his (Abraham's) sake alone, that it was imputed to him; 24 But for us also, to whom it shall be imputed, if we believe on him that raised up Jesus our Lord from the dead; 25 Who was delivered for our offenses, and was raised again for our justification.
HOLY SPIRIT A GIFT
Acts 2:38-39 Peter said to them, "Repent, and each of you be baptized in the name of Jesus Christ for the forgiveness of your sins; and you will receive the gift of the Holy Spirit. 39 "For the promise is for you and your children and for all who are far off, as many as the Lord our God will call to Himself."
Acts 10:45 And they of the circumcision which believed were astonished, as many as came with Peter, because that on the Gentiles also was poured out the gift of the Holy Spirit.