Perhaps the assignment was conceived not so that you would attend a group meeting which has explicit membership requirements which you do not meet ("Jewish professionals, Black Scholars") but to some event or location where there are implicit memberships. There are many event and location which have a different dominant group, but where the cause of the event is not for this group of people specifically to assemble. The problem is it is difficult to find and identify events not targeted at a population you belong to unless they are specifically labeled.
The best examples I can thing of off the top of my head are things like a discussion panel on community activism hosted by a local Black Baptist Church, would likely be attended primarily by members of that church, but would be open to anyone, and church membership would not be assumed. Or a public market in a predominantly Hispanic neighborhood, where most people would be Hispanic, and speaking Spanish, but being Hispanic would not be a requirement of shopping there.
I think being inserted into a group you are not a part of is stressful for anyone. I have great social skills, and I am pretty good at interacting with new people and I am not at all shy. I would still feel awkward as the sole out-group person in a group gathering. Realizing you are surrounded by people who are members of a group you are not a member of makes you hyper aware of where you sit within that particular social division. If you are a member of the socially dominant group it makes you suddenly aware of the comfort you might generally have in other spaces which get to be "yours" by default. If you are a member of a group which is not socially dominant, then your awareness about your lack of power increases. Because these situations are uncomfortable, many people avoid them altogether and that is a shame, since there are things to be gained by interacting outside of your comfort zone as it were.
I don't necessarily think the idea of the assignment was bad, but perhaps the specific instructions about how to go about finding a place to carry it out.