A HISTORY OF THE CONSTITUTION
The United States Constitution was constructed on September 17, 1787 after months of conflicting views, heated debates and clashing ideas finally yielded to compromise and thoughtful reconsiderations. The founders of the Constitution were delegates appointed by the state legislatures to represent each state's welfare. They had first convened in the Philadelphia statehouse as a quorom of 55 emissaries on May 25, 1787. Of the thirteen original states, only independent-minded Rhode Island declined to participate. The group's express original purpose was to revise the Articles of Confederation, our nation's first constitution that was constructed in 1777 after the Revolutionary War with Great Britain.
In theory you are correct that it is a creation of the people, but it was done through their representatives in much the same way as the people can amend it today. Speech, press and voting rights keep it functioning in the true interests of the people (at least that's the way it is supposed to work).
Written by a delegation and approved by state Constitutional Conventions (who I'm sure we can all agree are better representatives of the people than Congress).