Add multiple lines to a Field

Hi, I'm trying to add multiple lines into a field I created. What I'm trying to do is something like this: 

Since adding a gridview is not that easy at all, I started to add fields to complete with the information that I require. In some cases, an Account has more than one Contract, so I need to be able to add more than one field.

This is what I've done so far.

The problem about this is that I can only add one line, but i need it to be multi-lines. (Dates fields incluided too).

¿Is that possible? ¿Could anyone please help me?

Best Regards,