So here's my situation. I am an electrical engineering junior from India who had applied to various international research internship programs with no hopes of getting selected. There weren't that many projects in my line of interests for this one particular program but I went ahead and applied just for the sake of it. The project is on flexible sensors and the professor's whole research group and domain seems to be in material science and mechanical engineering. At the time of applying I hadn't done any research on his background and I just went ahead and applied anyway since I saw "sensors" and assumed the work would be in signal conditioning and that is something I am indeed interested in.

As part of the selection process, I had to send him a short write up about my background and interests and stuff . I did mention my work in sensor signal conditioning and indicated my interest in it but I also talked a bit about stuff I have no experience in. I think that it might have seemed like I knew what I was talking about in the writeup but I really don't. In my defense I really had no expectations of getting selected. Now I look at his work and research and it realize it's not relevant to electrical engineering at all. Without knowing the details of the project there's no way for me to know if the work would be something I can do. It's a very multidisciplinary field, so the professor might have something related to electrical/electronics in mind but I have no way of being sure.

I have until Thursday to accept the offer. I sent him a polite email informing him of my matching and asked him for more details. His response was very enthusiastic and it seemed like he assumed I would be joining him and said he would provide details later. How do I let him let him know that I want details before Thursday without sounding rude? Also is there a way to let him know that I have no idea about the mechanical/material science side of things but if there's work on sensor interfacing and signal conditioning I would love to do that? I feel really bad about this. This would be an incredible opportunity for me but if it's something I won't be good at then I would be wasting the professor's time and I possibly would have taken a good opportunity away from a student who would have been better suited for it.

Another thing is, the professor does have my CV and academic details and transcripts so maybe he went through all of that and did select me for a good reason but if he selected me based on my write-up alone then I feel he might have made a mistake. But I can't tell him that I don't think I am well suited for the project because then it would seem like I am questioning his judgement. Please give some advice.

There's another catch, I also have an offer from Texas Instruments which is indeed very relevant and I was very much looking forward to it. But my ultimate goal is grad school and I know a research internship would be more beneficial in the long run. So now I am very confused between the two.