Tamattaʿtu is the first-person singular perfect of Form V from the root m-t-ʿ, here “I enjoyed / took pleasure.” Min lahwin supplies the setting of amusement or pleasant company.
Ghayra muʿjal describes the circumstance. Muʿjal is a passive participle related to Form IV aʿjala, “to hurry someone.” Negated by ghayra, it suggests that the speaker was not hurried away.
The distinction between the main action and its circumstance matters. The perfect verb describes enjoyment, while the following qualification describes how the speaker presents that experience.