Why did bacon oppose the colonial government?

The government was being unfair to colonial farmers and Bacon and his men wanted to show the Continental Congress how strong farmers really were.

Not exactly. Bacon's Rebellion was in 1676, a hundred years before there was a Continental Congress. The Royal Governor, William Berkely, had pushed very high taxes through the colonial legislature, the House of Burgesses, which were perceived as chiefly having the purpose of enriching Berkely and his friends. When Indian trouble, largely instigated by white settlers, broke out on the frontier, Berkely proposed passive defensive measures which the frontier communities found inadequate. That led to the rebellion under Nathanial Bacon. Thus it was the two issues of unfair taxation and inadequate defensive measures that caused the uprising.