For pursuing MBA you need to start preparing for MBA exams like CAT, XAT, CMAT etc.  As you are unprepared right now so I will recommend you to prepare for 2018 exams because you are a pretty late and already have missed a lot of exams. So you will have a narrow chance of ending up in a good chance if you try this time.

After giving any MBA exam every college prepare a merit list to call students for next round of interview and WSAT based on your aggregate score which comprises of many factors such as CAT marks, 10th 12th and graduation percentage, work experience, engineer or non engineer, gender with different weightages for different colleges.

So with your 3.5 years work experience you will get an advantage durung selection process and also later in the final placements procedure.

So in short start preparing for MBA exams going to happen next year. Aim for a high percentile and convert a call from good college.

All the best!!