You need to complete and submit the FAFSA for each year that you attend school. Three years at school means completing a FAFSA three times.
The government accepts and processes FAFSAs well into the summer, but the schools you apply to will have more aggresive timelines. Be aware of your chosen schools' financial aid deadlines ahead of time and schedule yourself to meet them. (It is not uncommon for schools to require additional forms, as well.)
The graphic below represents the timetable described above.
