Dear Candidate,

No,you didn't required to get sign on any document by your school principal latest if he already sign all the documents for mbbs already but in futre if college demand some attested signature again of your principal then you again need to get sign of your principal on that particular document and this time they also gave some time period to you for that work.So,don't worry about that if you already do this earlier if something new documents your college want then they give time to you for that.

Hope,this helps you to get answer of your query.