The good news is if you mess up in your first year, you learn and remember not to mess up in your final year with your dissertation project. The first year of uni is all about making mistakes and learning from them.
Regarding the word count, you should be about -10%/+10% near the word count. Some unis have it as 5%. Check the assignment specification. In my first year, word count didn't really matter as long as you were in the range. In my final year, I lost marks because of the word count.
Anytime you use a source, reference it. Anytime you say something factual, reference it. When I was studying humanities, my teacher at the time said to always check whether every 100 words or so I have at least 1 reference. In the science field, my professor said every time you mention a fact drop a reference. In my second year, I didn't cite where I got a certain diagram (it was obvious that I didn't create it) so my professor commented on it in my feedback and I wasn't able to get higher marks because of my citations.
Overall, based on my experience in my uni, I think that the consequences would mainly be a note written in your feedback that you haven't completed proper citations & havent met the word count. In the event that your grade for this paper is less than a D (40%), some unis will allow you to retake the assignment but this is subjective from uni to uni.