This feels self-flagellating, and after reading your family planning vs animal welfare piece, in which you spent 26% of the word count explaining why your analysis was bad despite pretty much all of the comments being positive, and which I  think was really valuable, I am a little worried you might be underselling yourself. 

As Charlie's said, it is a little tricky for an outsider to know what you're capable of without more information. I don't want to be unrealistic and suggest that you'll be able to do whatever you set your mind to, but I would note that aptitude is not fixed.

If it would help to have some back and forth with someone, feel free to reach out.

A lot of the advice for young EA's is reasonably targeted at folks much more impressive than I am, for good reasons I think

Assuming you have, but still probably worth skimming the earn to give sections of 80k/probably good and looking at their job boards. 

Hard to say more without knowing your interests and how "mediocre" you are. You can sign up for career coaching with 80k and/or probably good. Also, it could be useful to reach out to other ea students studying math at other universities and talk to them. can query link below by career stage. 

https://forum.effectivealtruism.org/people-directory?utm_source=ea_hub&utm_medium=website

If you want to informally bounce ideas around about potential careers, I think that there are a number of people who would be willing to spend 15 to 30 minutes speaking with you and sharing thoughts on skills, training, career paths, etc. Not as some kind of paid scheme, but just people willing to help out a little bit. You can certainly reach out to people in your own life (relatives? professors?), but there are also quite a few people in the EA community who are willing to do this.