Why can't I add columns to my database?

from peewee import *

db = SqliteDatabase('students.db')


class Student(Model):
    username = CharField(max_length=255, unique=True)
    points = IntegerField(default=0)
    email = CharField(max_length=255, default="test")
    password = CharField(max_length=255, default="test")

    class Meta:
        database = db

students = [
    {'username': 'chrisgunawan',
    'points': 4888},
    {'username': 'chalkers',
    'points': 11912},
    {'username': 'joykesten2',
    'points': 7363},
    {'username': 'craigdennis',
    'points': 3444},
    {'username': 'davemcfarland',
    'points': 1412},
    ]

def add_students():
    for student in students:
        try:
            Student.create(username=student['username'],
                        points=student['points'])
        except IntegrityError:
            student_record = Student.get(username=student['username'])
            student_record.points = student['points']
            student_record.save()

def top_student():
    student = Student.select().order_by(Student.points.desc()).get()
    return student

if __name__ == '__main__':
    db.connect()
    db.create_tables([Student], safe=True)
    add_students()
    print("Our top student right now is: {0.username}".format(top_student()))