Hi Ashutosh,
Before clicking the link "SAP HANA web based development workbench", did you try opening the link "SAP HANA Cockpit" with the SYSTEM user and password you provided when creating the MDC Database (as mentioned in my previous response).
When you are in the Web based tool, you do not need to use your HCP account username and password. You can use your SYSTEM user or any other DB user which you create later on.