It is not possible to learn a complex skill just by reading and following some instructions. In fact, nobody would be able to write such instructions in a complete way. Instead, it becomes more important than otherwise to engage in the task - in our case to solve modelling problems - to make experiences, and then to learn by reflecting over these experiences. The reflective step is a key aspect of the principle of "learning by doing". It can help you to make observations and generalizations, and become more aware of your own thought processes.
Then, when you practice with the purpose of developing a process such as your problem solving ability, it makes little sense to only consider the end result. You may have learned a lot when you struggled, independently of how experienced you are or how close you came to a solution. So what you have learned is relative - you have improved. This is the most important aspect, because if you know how to improve and continue to do so, you can in the long run reach any reasonable level.
However, it is also natural to consider - and good to be aware of - your absolute level of performance at different times. This is what we usually do to confirm professional ability, and in school when we pass tests and set grades.
So how self-assess a module submission? You need to find your own way, but I can possibly be helpful by describing how I tend to think about this.
My overall idea - which is useful far beyond the assessment of course modules - is to try to roughly characterize qualitative notions of "insufficient", "sufficient", "good" and "very good" performance. It is of course possible to use other labels.
In a school setting, the most common way to do this is to simply consider the ratio of correct or almost correct answers. Getting almost all solutions right would be "very good", and we would use some lower fraction for "sufficient". What that lower fraction should be is usually arbitrary - maybe 50% if some problem solving is involved, maybe 80% if it is mostly about basic facts. If you want to think in this way that is fine. However this simple way to assess breaks down if we consider the quality of a report, work with projects, or deal with tasks that have no correct answers, such as design. There may still be ways to characterize a good result, but sometimes this can be difficult or impossible to specify.
Another way to think is that an "honest" effort is good enough - that I have done my best given my current abilities (and the time available). This notion of acceptance is inevitably more relative, but I think it makes a lot of sense in some situations, especially in an educational setting where a complex skill or process is to be learned, and especially in the beginning. If I do my best am likely to learn a lot. And if I do so over a period of time, I will - if I am not the wrong person in the wrong place - most likely develop adequate basic skills and insights.
I would then say that I have made a sufficient basic effort if:
And I then find it less important if:
The idea of an honest effort can however still include some absolute quality considerations, in that there should be no weaknesses that are easily avoided with a careful attitude to the work. So examples of an insufficient effort include:
Then what would characterize a very good performance? We must here inevitably focus on good solutions, allowing this to become a matter of subjective judgement as necessary. Additionally, we may expect that everything around the solution should also be good. This makes some sense since if we consistently work with good processes, values and attitudes, we will increasingly succeed with even more challenging problems. So we could consider:
I find it reasonable to think that for a "very good" performance, these qualities should be present to the highest level that can reasonably be expected given the circumstances. Note that there is a very large variation in how this can be achieved and where the emphasis is. Then, for a "good" performance, these qualities should be clearly demonstrated to some extent.
Finally, be aware that it is not possible to see these criteria in a strictly literal way - an interpretation is required. You should take care to understand what I have written, but however I write it will not be perfect, complete, or true in any absolute sense. You may additionally have your own well-founded views about how to think. So it is ultimately about developing your own sense of judgement. And this is an important skill for your ability to guide yourself in your studies and in the future.