Was the Constitution a fulfillment of the Revolution or a reaction to its excesses?

Primarily, one would have to say it was the latter. The American colonists' struggle against the British imbued them with a radical republicanism deeply suspicious of centralized authority and committed to the ultimate political sovereignty of the states. This governing principle formed the basis of the Articles of Confederation, which established a loose, decentralized structure of government consonant with the spirit of the Declaration of Independence. The Articles of Confederation achieved two notable successes. First and foremost, they enabled the Americans to prevail in the Revolutionary War. Secondly, they made it possible for the Americans to conclude a peace settlement with the British at the war's end.
The Articles of Confederation may have helped Americans win the war, but they could not help them win the peace. The loose, decentralized structure of government was simply too unwieldy for the monumental tasks ahead. For one thing, without a centralized government, the United States was unable to pay off the enormous debts it had accrued during the war. Also, territorial disputes with foreign powers dragged on, as they could only be dealt with at the state level. As law and order were the exclusive province of the states, domestic disturbances could easily get out of control and spread across state lines. Indeed, it was one such disturbance, Shay's Rebellion, that was the single most important factor behind moves to establish a new constitution.
Supporters of the Constitution, or Federalists, were every bit as committed to the principles of the Revolution as their Anti-Federalist opponents. It is just that they felt that embodying those principles in a stronger, more centralized system of government was a better way of ensuring that they endured over the long term. Anti-Federalists such as Thomas Jefferson represented the republican spirit of the Revolution, but it was the likes of Alexander Hamilton and other Federalists who sought to give lasting substance to the “spirit of '76” while curbing some of the notable defects of the Articles of Confederation.