Can I hope to convert an IIM Calcutta call with a CAT percentile of 98.85?

When it comes to the final decision, your CAT score only has a 30% weightage. Your WAT and PI scores are heavily weighted, with only a minor weightage given to Academic Diversity and Work Experience. So it all depends on how well you do in those.

You can be optimistic, but if there is someone doing equally well on all other fronts as you while having a higher CAT score than you, the institute will obviously prefer them over you. There is so much competition out there that you cannot afford to lose points anywhere, especially at IIM ABC. To give you an idea, there are many students who do not receive an IIM Calcutta call despite having a 98.90%ile and 10, 8 academic scores.

To summarize, do your best and hope that not many people perform better than you, and you will have a converted call from IIM Calcutta.