Listening is indeed mostly a matter of practice and there is little you can do if you have an exam next week. Improving listening ability takes a lot of time and short-term cramming won't help. I'm going to separate this answer into two parts: one short-term and one long-term.
In the short run, you can do a few things to improve your chances of passing, such as making sure that you are very familiar with the test format, but it seems you have already done this (the online practice tests).
The biggest problems with trying to pass listening tests that are actually above your level is that it's very hard to concentrate when you lose several words each sentence. Try to focus on what you do understand and don's zone out.
Make sure you read the questions in advance so you know what you're listening for. Take notes if the dialogues are long. If you can't write in characters fast enough, I suggest writing in English. You don't want to waste mental effort on writing notes and thereby miss the next sentence.
Now let's talk about listening ability in general (which won't help you pass this exam, but should help you pass the next). The first goal is to figure out what your weak link is. Simply knowing that you don't understand the audio isn't good enough. What causes it?
Here are a few possibilities:
- Lack of phonological awareness
- Lack of vocabulary
- Lack of listening speed
The first is about understanding syllable and word structure, including being able to separate all possible syllables, tone combinations and so on. Can you map the sounds you hear to the words you have learnt? If you mistake certain sounds for other sounds, you need to sort this out first.
The second isn't really about listening, but I think it's still one of the main reasons why it's hard to pass at least standardised proficiency exams. They don't (only) use the words you've learnt in your textbook, so you will encounter tons of near-synonyms you aren't as familiar with. The solution is to study broader rather than deeper. Study more material at or below your current level. Not more advanced stuff, just more.
The third problem is speed and it's common for all except those who take immersion very seriously. Even if you can map all sounds and know all the words, the audio might simply be too quick for you to understand. It's not enough to be able to understand a word, you need to be able to do it fast. The only way of increasing speed is to listen a lot. If it takes you two seconds to remember what a word means, the voice will be halfway into the next sentence.
How to practise, what to improve
You should obviously study differently depending on which of the above is your main problem, but simply listening more will improve all three areas described above. Vocabulary is somewhat different, but listening more will expand your vocabulary too. Make sure you always have Chinese audio easily available. Listen when you drive, walk, cook, exercise, fall asleep, brush your teeth, wait for the bus and shop for groceries. It will be demanding in the beginning, but you will soon get used to it. You will be richly rewarded.
In case you want more advice, I have written a series of articles dealing with listening ability (I hope it's okay to link like this, it's simply way too much to write here, but still very much on-topic).