Raspberry Pi header pin 7 is labeled as WP_GPIO_3_lvl in the schematic which can be traced to WP_GPIO_3 and finally to GPIO24 on the “outer ring” of the cf3 module. So 24 is the GPIO number that you want to use in your code. Aside from that, your code won’t appear to do much because you turn the GPIO on and then immediately turn it off.
Maybe take a look at the heartbeat app for a demonstration of LED blinking.