I know it's very hard to maintain your fitness after stop gymming. But I can suggest you that you should maintain your proper diet.
Here , I have an application for you which will help you to maintain your fitness. "MyFitness Statistics:Weight Loss & BMI Calculator" is an application that monitor your daily fitness & health statistics.
The application will provide different reports like BMI, BMR, Body Type, Ponderal Index and many more. Moreover, the application will guide you how to maintain health according to your reports. So, now you can easily track your daily fitness and can maintain it.
Hope, this works out for you!