math major concerns about research internship

So I'm a freshman math major studying at a target interested in investment banking. I've been contacting a lot of boutique investment banks and one has responded indicating that he might have some research for me to do (possibly a little bit of modelling in the future). Could tell he was clearly in a bad mood from the beginning and he kept stressing that this would 99% be an unpaid internship and I would also be doing a lot of grunt/administrative work. 

So my major concern is unequivocally not the fact that it's unpaid nor is it that the work is mostly administrative/grunt but that I'm a math major and may have to produce lots of reports. I have the next week to decide if I want to accept this unpaid internships (I understand any experience is valuable), but again, I am concerned that I will be writing reports given that essentially although super confident in math couldn't say the same about english.

To be honest, I have read about ~20 books in the past year but probably wrote 1 practice essay in the last 4 years. So clearly, I understand that writing is my weak point that I am trying to address

edit: so I got a bad vibe with this interview and ultimately didn't want to pursue it. My only other interview I had went well because the CEO was a stem major and looked highly on my math background (im math/econ/finance btw) and that was ultimately the reason I got it