You have graduated, and now have a Bachelors degree.

Now you are bachelor. If you continue studying - you will specialist or master.

(You now have a bachelor's degree.) If you say "I'm a bachelor"=solteiro

Finishing four years of study does not necessarily mean graduation. Some requirements may remain unsatisfied. After graduating, one receives a bachelor's degree. You might also refer to the graduate as a bachelor, but that is ambiguous and not commonly used.