Django registration form not changing and saving to database

Question

I'm trying to create a custom form where the user can also enter his name for instance but I am facing an issue, when the registration is done the name is not saved and I can't show it on the template. here is the code:

views.py

def sign_up(request):
form = forms.SignUpForm()

if request.method == 'POST':
    form = forms.SignUpForm(request.POST)

    if form.is_valid():
        email = form.cleaned_data.get('email').lower()

        user = form.save(commit=False)
        user.username = email
        user.save()

        login(request, user)
        return redirect('/')

return render(request, 'sign_up.html', {
    'form': form
})

forms.py

class SignUpForm(UserCreationForm):
email = forms.EmailField(max_length=250)
first_name = forms.CharField(max_length=150)
last_name = forms.CharField(max_length=150)

class Meta:
     model = User
     fields = ('email', 'first_name', 'last_name', 'password1', 'password2')

def clean_email(self):
     email = self.cleaned_data['email'].lower()
     if User.objects.filter(email=email):
         raise ValidationError("This email address already exists.")
     return email

sign_up.html

<form method="POST">
       {% csrf_token %}
       {% bootstrap_form form %}
       <button type="submit" class="btn btn-warning btn-block">Sign Up</button>
       <p class="text-center mt-3" >
       Already have an account? <a href="/sign-in/?next={{ request.GET.next }}"><b>Sign In</b></a>
   </p>
</form>

The html is showing me also the username, which i wanted to remove and login with email address. But nothing gets saved in database...