Is it wrong to make assumptions if you're a scientist

No. You just need to have a scientific basis for your assumption. You need to give some evidence why your assumption is probably correct, then explain why your assumption does not significantly affect your result. If you verify your theory with experiments and the results agree, the assumption is probably safe.

Pretty much any numerical simulation or simple analytical expression relies on some simplifying assumptions. You just need to be aware what the assumptions are. One of the downsides to using journal articles as references (vs a reference book) is that you tend to get third, fourth, fifth-hand accounts of certain procedures or analyses. Rather than referring to the original paper, people cite the more recent one, and parts of the original process or derivation, like the underlying assumptions, get forgotten about like a game of telephone. Then people start using it for things it wasn't intended for and the assumptions no longer hold.

No it is not wrong to make assumptions. If you make a assumption and you get a result and that result is right than it indicates that your attempt was successful. Your assumptions will be treated correctly as long as result coming out of it is correct (that it matches with experimental data or something like that)

Some things you just have to assume because it is physically impossible, or very difficult to find out the truth. Don't worry though, the assumptions are based purely on research.

I'm not certain you understand what science is and how it works. You also are wildly incorrect in the things you say here.

There are ZERO scientists in history that have never made an assumption. We are not machines.

Yes you can to do it as scientist yet. And so your classmates But your idea ought to be proved.