Cumarteside alışveriş merkezide sen gördim. Thank you . I saw you on Saturday at the shopping centre . Thanks

I´ll try to help a little here:

"Cumartesi günü alışveriş merkezi(n)-(y)e seni gördüm."

Hum....not sure about which buffer to use, if it is to use the genitive or dative. I would say it´s dative here, thus merkeziye.

Wait for advanced learners or native speakers corrections please, they´ll be better.

...merkezinde....

Thanks zeytinne.......when I tried to say it, it sounded more ´natural´ to say ´merkezinde´......

but when I started writing it.......another story, struggling with my grammar!

Thank you for your corrections!