Just going to address a few more of your concerns

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Yes, I am quite nervous for the exam. Mostly because of the time constraint
You can look to tackle this issue in a few different ways. Some of my friends who did do better than me did daily rigorous practice under timed conditions, while I took time pressure out of the picture completely, and just timed myself after doing a set of questions (without worrying about time as any sort of constraint) or even just in a chill untimed way. What's important to note here is that there is no one way to succeed - you can try one of the above two ways, none or both and any number of them could work!
Some important considerations:
- Ask yourself 'how do I function best in a school-based exam?' - this will give you some sort of measure as to how you already cope with time pressure -> think particularly about exams where you have to write (time constraints are particularly tight here) or mathematics (relevant subject matter).
- Not completing all the questions in practice is not something to worry about - if you're getting close enough to finishing in the time limit, that's excellent; you do tend to go a tad bit quicker in the actual exam and you'll probably finish with an exam adrenaline rush type thing
- Even if you're not close, it's important to note that you should focus on maximising the marks you can get instead of maximising the marks you can't -> just get as many questions as you can right in the time limit over finishing all the questions

I am trying to do thorough preparation - a bit during the week and then lots on my weekend and then I'll have two weeks I can completely devote to UCAT in my holidays. I am purely using the free UCAT resources on the website as well as free video tutorials as I decided not to rely on external providers. Hopefully, I can still do well without relying on external resources (and UCAT stressed that they don't endorse these so I'm following with that).
I never paid for anything either - it's so crucial to see just like how in school effort =/= marks, money spent =/= higher UCAT score. What's more important is how well you understand what the questions ask, how focused you are and how well you can cope with pressure. If you can do that without spending any money and you can back your own ability, you'll do better than almost everyone that pays to succeed, and everyone will think you're 10x cooler for a bit - you can 110% do well without relying on external resources.
Would I be right in saying, you try and finish the whole test but maybe you have to make guesses for the rest you don't finish due to the time pressure?
Typically, as soon as you see a question you can't answer quickly, you skip it, and come back at the end - for verbal reasoning, you tend to skip the whole question set since you don't want to have to read the passage twice, synthesise it twice for two separate attempts at different questions in the set. This holds true for abstract reasoning particularly, since the time you get is literally criminal.
If you do find yourself running out of time, you should guess - it is better than putting nothing down at all. It's always good to be glancing at the time remaining frequently to know when you need to up the ante a bit - depending on your confidence with each section, it might also be a wise decision to start making educated guesses earlier than making random guesses when you're really running out of time.
Also, did you find the actual test to be very similar to the practice tests in terms of difficulty and question type similarity?
It actually depends. I think in my year there were three different tests in rotation and you got one of the three. Some companies apparently had tests which were bang-on in terms of difficulty, but for all the F2P people, the UCAT website did an excellent job compared to the majority of companies who were basically clueless in the first year of UCAT. I don't remember the UCAT tests as well as the actual exam, but I do remember feeling more confident the more I went through the exam, and that they were reasonably similar enough because at no point did I actually get thrown off. At any rate, all practice is good practice, if it helps you understand the concepts better.
Hope this helps
