The font used for "Arabic calligraphy gallery" doesn't really suggest calligraphy to me. Think about using a font that captures more of that "hand-written" aesthetic. Also think about reducing the size of the text for the gallery location and breaking it into 2 lines and centered. Also consider spelling out the dates (i.e. Feb should be spelled out as February). This will make it look and feel more formal. I don't know what your final poster size will be but also consider making a vertical list and centering the artists names - almost like movie credits. Hope this helps.