Welcome KittiPaws! Congratulations on taking your first steps toward better health and fitness. It's not your bike, it's the re-entry into fitness. You said you have pretty flat land so you should be fine. In time you may want to upgrade if you find you love the sport and what it does for your body, and want to ride miles and miles on end. Until that time just keep up your good work so far. A couple of blocks turns into a mile and one mile turns into 2,3,4,5 and so forth.

The huffing and puffing will stop and you will amaze yourself with your abilities. I love falling in love with bicycling. Enjoy your re-entry into biking and have fun out there!