Hello! Welcome to the game!
Using seeds from Nooks Cranny is actually the best. But even watering flowers for a week doesn't guarantee a hybrid.
There is a hidden counter that increases each time you water the flower, and watering for a week still only gives you around 25% chance of the flowers reproducing.
To speed things up, you can have visitors also water your flowers.
You can also enact the Beautiful Island Ordinance. Make sure you're not digging up the flowers, because that resets the water counter.
And your English is great! Many people on this forum only know English as their one language, so please don't ever feel like you have to apologize for learning a new language. ☺ The flower breeding stuff can be really confusing, and there's a lot of incorrect information out there, so please let me know if you still have questions.