Why is cleaned data returning an exceeded value length from the registration form?

Question

I have a custom user model that has a username field with a max_length=50. Under the custom registration form, it throws me an error when the value of the username` field is just less than 10 characters:

Ensure this value has at most 50 characters (it has 170).

Below are the codes that I used that is in correlation with the username field:

#models.py
class UserAccount(AbstractBaseUser, PermissionsMixin):
    username = models.CharField(null=False, blank=False, max_length=50, unique=True)

#forms.py
class RegisterForm(UserCreationForm):
    username = forms.CharField(widget=TextInput(
        attrs={
            "class": "form-control",
            "id": "username",
            #"placeholder": "Username",
        }))

    class Meta:
        model = UserAccount
        fields = ('username',)

    def clean_username(self):
        username = self.cleaned_data.get("username")
        username_filter = UserAccount.objects.filter(username__iexact=username)
        if username_filter.exists():
            self.add_error('username', "Username is already taken")
        return self.cleaned_data

HTML

<div class="row form-group">
    <div class="col-sm-4 label-column">
        <label class="col-form-label" for="username-input-field">Username </label>
    </div>
    <div class="col-sm-6 input-column">{{register_form.username}}</div>
</div>

The error only occurs when I use the registration form on the html when creating a user, but when I create the user via python manage.py shell and admin panel, it gets created without any error.