Showing initiative

Hi,

So I have managed to get a boutique internship beginning of january where I will also be working on my thesis.

Last week, one of the partners comes up to me and starts talking about an assignment I didn't do well. The assignment was something I had never done and I didn't know where to find the required info. Next he goes on about how I don't shown enough ambition and that I don't take initiative. Which I thought I was doing....

I had an informal internship last year and just came back from my exchange program before starting this internship. Besides, I have a leadership position in a voluntary organization.

So my question is, how do you show (more) ambition and take initiative??

Please provide me with some constructive feedback :).