Nothing went wrong per se, it’s more likely that no one told you about the expectations of college level writing or you were too nervous at orientation and weren’t listening. Whatever it was, here you are now wondering how to write an essay that’s acceptable in university.
The key to a good descriptive essay is to really dig into the five senses as they relate to the subject of your essay. For example, if your essay is about a trek in the forest you’d focus on the senses of touch, smell, hearing, and sight, maybe not so much on taste. A well crafted descriptive essay will allow you to share a picture of something as vividly and as genuinely you can and to transport your reader into experience where they feel that they are actually seeing, hearing or experiencing it themselves.
When talking to students, most often they will recognise that they might struggle with a particular aspect of writing. Most often they'll say things like "my grammar sucks" or "my instructor just doesn't like my writing style" or "my teacher just wants me to repeat from class."