Well, hitting the back brake hard would only likely cause you to skid or fishtail if there's any sand on the road (which I imagine there's still tons in the city, as it is out here on the island), which might end in you falling over sideways. You were probably okay using the front brake only, but you need to initiate a weight shift to stop yourself going over the bars. To do that, you need to both push your butt further back on the saddle, and put some 'pushing' force into the handlebars. You may need to adjust your brake or pads for better modulation if it's too grabby. Read this link, Sheldon explains it better than I can.

Hope you get better and can get back on your bike soon.