I'm suprised at how many people who have studied Psychology in this thread have said that they had to design a research study but didn't have to actually carry it out. For my undergraduate (in Psychology) and Masters (in Health Psychology) degree courses, conducting our own research project by designing, recruiting participants and writing up the study was the main assessment. Maybe it's different in the United States?

Regarding ethics, whether you intend to get your work published or not is irrelevant, you still need ethical approval when using human participants. Maybe your professor has already had it approved for the whole class, but since you are designing your own study I don't think that would be the case... But anyway, how is your project going? Have you thought about what statistical analysis test you are going to use to analyse your results? Reading your brief description it seems you would have to conduct a One-way between subjects ANOVA since you are planning on having three groups with different participants for each group. (Remember you would need quite a lot of participants for such a design). It's very important to know what statistical test you are going to use before actually doing the study.

For my Masters project, I assessed health behaviours (smoking status, alcohol consumption and physical activity engagement) on perceived future health risk (e.g. perceived risk of developing CHD and cancer). Basically assessing whether people who live an unhealthy lifestyle perceive to have a higher personal vulnerability to CHD and cancer. I used a questionnaire design and although I don't like questionnaires since I don't find them particularly reliable, it is the easiest way to get a larger sample size. For my undergrad project I carried out a lab study and it was such a chore to get the participants and bringing them back to the lab! lol.