I think it is fine. If you wanted to say that it is your embroidery as opposed to something someone else made, you could say “ I embroidered this when I was…..

It's correct.

I/We/You/He/She/It/They made this embroidery when I was in university. (Active Voice). This embroidery was made by me/him/her/them when I was in university. (Passive Voice). You wrote a correct sentence in a Passive voice. In Passive voice, it is not necessary to mention the agent who is doing an action

The grammar is perfect. Many Americans won't know what "uni" is, but Canadians and British people will understand. (Americans usually say "college." But that is just regional vocabulary.)

Yeah it's good. In the United States we would say "college" instead of "uni".