The answer to this question revolves around what you mean by “ill-prepared.” Depending on how you define this, it is possible to argue this either way. (Since your question asks about George Washington, I will discuss him as an individual rather than the colonies as a whole.)
In one sense, George Washington was very ill-prepared to fight against British forces. Washington was being asked to function as the commander-in-chief of a colonial army that was about to fight a large-scale war against one of the strongest armies in the world. Washington did not have any sort of experience or training that would have made him well-prepared for this task. He was arguably the most experienced American officer because of his participation in the French and Indian War, but this hardly prepared him to lead a major army against a European foe. In the French and Indian War, he led a single regiment in backwoods conditions against a foe that was not much like the regular British Army. In this sense, he was very unprepared to take on the role of commander-in-chief of a large army and to fight the British forces.
In another sense, however, we would have to conclude that George Washington was prepared to fight the British forces. The proof of this is in the fact that he led the Continental Army to victory. His actions in the war prove conclusively that he had the attributes needed to succeed in his role. He had the ability to keep the army together, to devise a winning strategy, and to adjust to changing circumstances. These abilities allowed him to lead his side to victory.
On paper, George Washington was ill-prepared to fight the British forces because he lacked the training and experience for the task. However, he clearly was prepared in that he had the attributes (even though he had not been formally trained) that were needed to lead the colonies to victory.
I wouldn't say that George Washington and the American army were ill-prepared; I would instead say that they had poorer circumstances than the British. First of all, the American army lacked funds, including proper attire and other supplies such as food and medicine. In addition, they lacked training. They also had fewer soldiers, as at least 20% were openly loyal to Britain. The Americans lacked a real navy as well. Compared to the British, who had properly trained and equipped soldiers, enough funding, and arguably the best navy in the world, it can definitely be said that the Americans were at a disadvantage. However, that doesn't mean that the Americans didn't have advantages over the British. They had a cause— a reason— to fight, which helped them pull through despite the circumstances. They also fought on their own country, which worked in their favor as they knew their own land. The British sailed a long way to get to America, which caused many soldiers to be in poor condition due to sleep deprivation and exhaustion.