Python modules I've just installed in my virtual env, are not found – Ubuntu

I’m using Ubuntu 20.04.5 LTS. Output of python3 --version command: Python 3.8.10
When I type pip in terminal and press TAB, it responds with the following options: pip, pip3, pip3.10 and pip3.8

But, when I use any of then with the --version flag, it all prints the same output, which is: pip 22.3.1 from /home/myuser/.local/lib/python3.8/site-packages/pip (python 3.8)

When I use "pip list" command, I can see the "virtualenv" package version(which is 20.17.0)

Then I create my virtual environment using this following command: python3 -m venv .env

Then I activate it using source .env/bin/activate command

Before installing the modules, I update virtual environment’s pip, using the following command:

.env/bin/python3 -m pip install --upgrade pip

Also, I have a file called requirements.txt with the packages names I need in it:

wheel
numpy
matplotlib
sklearn
seaborn

So I install them using the following command:

.env/bin/pip install -r requirements.txt --no-cache-dir --use-pep517

Finally, I try to run my python program using ".env/bin/python kmeans3.py" command, it prints this error:

Traceback (most recent call last):
  File "kmeans3.py", line 10, in <module>
    from sklearn.cluster import KMeans 
ModuleNotFoundError: No module named 'sklearn'

obs: This is the first 12 lines of the file:

"""
.env/bin/python3 -m pip install --upgrade pip
.env/bin/pip install -r requirements.txt --no-cache-dir --use-pep517
"""

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt 
import seaborn as sns
from sklearn.cluster import KMeans 
from sklearn.metrics import silhouette_score
from sklearn.preprocessing import MinMaxScaler