only create 3 topics

It should create 11

randomly it is creating three topics

Yes, those are internal topics for utilities.

can anyone explain what does tasks.max property do?

For JDBC source - nothing, since it is limited to just 1. Otherwise, imagine if you were using MirrorMaker2, then the tasks should equal the amount of partitions to distrubue

Suggest reading through https://docs.confluent.io/platform/7.1/connect/concepts.html#connectors