The Compromise of 1850 did not settle the question of whether or not future states admitted after California or Texas would be slave or free states, it merely provided the means by which it would be determined. Popular sovereignty was included in the Compromise, which meant that each state admitted after 1850 would also have a vote on slavery, where the majority would rule. Of course, this led to the disaster known as Bleeding Kansas, and no state was ever able to carry out popular sovereignty.
In addition, the Compromise supposedly strengthened the Fugitive Slave Act, which required law enforcement officials in the North to arrest and return any slave found to have run to the North, under punishment of heavy fines. The compromise, however, provided no way to enforce such a rule, which was always the problem with the Fugitive Slave Act.