Both are really interesting careers! I have found in research there isn’t much difference between them, there are people with lots of different backgrounds working in my office on the same projects – from medical doctors, to criminologists, physicists, material scientists, engineers – nobody studied biology at University and yet we all work towards making improvement to medicine.
So yes I would recommend being an engineer or a scientist, it can be fun and rewarding, but don’t get too hung up on which too early. Study lots of science and maths and you can do which ever feels better for you.
As Sophie mentioned above, you don’t have to worry that training in a specific STEM field will lock you into working in that field permanently. I was a scientist and now I work as an engineer.
I worked as a lab scientist first, using big lasers and vacuum chambers to study very fast chemical processes and their products. Working as a scientist also means a good deal of pressure to publish, however, and I found I didn’t enjoy that as much as the actual research. Switching to a space engineering career allowed me to spend my time in the lab without the need to publish constantly. I’m now working mostly on electronics boards and small metal boxes. I do occasionally miss the fun of hauling around giant gas cylinders and the whirr of constantly running pumps, but I’m still quite happy because the work I do is facilitating the exploration of the outer planets!