No, you are wrong! The Kingdom of God and the Kingdom of heaven are the same thing.
Most of time Mark, Luke and John use "kingdom of God," they are referring to the same thing, the Kingdom which Jesus initiated.
Matthew, on the other hand, uses the phrase, "Kingdom of heaven" as the same thing as the other 3 gospels call the "Kingdom of God." Why the difference in terminology?
Luke wrote his gospel to Theophilus, a Greek. Mark was likely Writing to Gentile converts, as he stops to explain various Hebrew and Aramaic terms. John wrote to Ephesians Gentiles. That leaves 3 gospels being written to Gentiles.
The exception to that was Matthew! It was written to Jewish Christians, probably located in the Jewish homeland. Jews abhor saying the name of God. You may see people who are Messianic Jews, use G-D, leaving out the vowel. But a better way for a Jew to avoid using the word God, was to change it to another word. IOW, heaven means God.
Looking at parallel passages confirms this!!
"Mark and Luke used “kingdom of God” where Matthew used “kingdom of heaven” frequently in parallel accounts of the same parable Compare
Matthew 11:11-12 with
Luke 7:28;
Matthew 13:11with
Mark 4:11 and
Luke 8:10;
Matthew 13:24 with
Mark 4:26;
Matthew 13:31 with
Mark 4:30 and
Luke 13:18;
Matthew 13:33 with
Luke 13:20;
Matthew 18:3 with
Mark 10:14 and
Luke 18:16; and
Matthew 22:2 with
Luke 13:29. In each instance, Matthew used the phrase “kingdom of heaven” while Mark and/or Luke used “kingdom of God.” Clearly, the two phrases refer to the same thing."
https://www.gotquestions.org/kingdom-heaven-God.html
"Within the universal kingdom of God, however, there are other concepts referred to as kingdoms. Principal among these are the kingdom of God, found seventy-two times in the New Testament, and the kingdom of heaven, found thirty-two times, all in the Gospel of Matthew.
A comparison of these features of the kingdom of heaven and the kingdom of God reveal many similarities: (1) both are at hand; (2) some features of both designated mysteries; (3) both entered only by the righteous as even profession requires outward conformity; (4) both include saved men; (5) both grow rapidly; (6) both have “birds” representing Satan and his angels, but in neither are these an organic part of the tree; (7) individuals in both likened unto children; (8) both are difficult to enter; (9) both have leaven, symbolic of bad doctrine, externalism, unbelief, and worldliness; (10) both contain Gentiles.
Because of the similarity of the two kingdoms and the fact that heaven is sometimes used as an equivalent for God, the majority of scholars have taken the position that the terms are identical or at least are used as synonyms. Based on the principle of interpretation that the context must determine the meaning of an expression, it would seem clear that in parallel passages the emphasis is on similarity of concept."
https://bible.org/article/kingdom-heaven
"
While some believe that the
Kingdom of God and Kingdom of Heaven are referring to different things, it is clear that both phrases are referring to the same thing. The phrase “kingdom of God” occurs 68 times in 10 different New Testament books, while “kingdom of heaven” occurs only 32 times, and only in the Gospel of Matthew. Based on Matthew’s exclusive use of the phrase and the Jewish nature of his Gospel, some interpreters have concluded that Matthew was writing concerning the millennial kingdom while the other New Testament authors were referring to the universal kingdom. However, a closer study of the use of the phrase reveals that this interpretation is in error.
For example, speaking to the rich young ruler, Christ uses “kingdom of heaven” and “kingdom of God” interchangeably. “Then Jesus said to his disciples, ‘I tell you the truth, it is hard for a rich man to enter the kingdom of heaven’” (
Matthew 19:23). In the very next verse, Christ proclaims, “Again I tell you, it is easier for a camel to go through the eye of a needle than for a rich man to enter the kingdom of God” (verse 24). Jesus makes no distinction between the two terms but seems to consider them synonymous." (Got questions.org)