@sydney can I throw in another option? May not be a popular view on a cycling forum but I feel you would continue to get fit and lose weight quicker by walking rather than cycling.
An inner city 3.5 mile bike ride is just that, it will be stop/start, slow/quicker and unlikely to raise the heart rate. The difficulty is such a short ride doesn't give you any sustained effort.
Walking pace of +3.5 miles will give you almost an hours sustained effort and slightly raised heart rate. Both excellent for weight loss and fitness.
I ride three times a week, 150/170 miles a week. On the days I can't ride I try to walk for one hour at +3mph which I see as a form of recovery exercise from the far greater exertion of riding 70 miles.
You may want to carry more, reduce the time etc. but if fitness and weight loss was my only target I would walk.
Consider investing in a pair of quality walking shoes.