If it says 4.3 on the reader you need a blood test to confirm its above 5 as you believe it is.
Absolutely. The libre can be very inaccurate, all the time for some people, some of the time for others, and is particularly known to be dubious at hypo levels. There's also the issue of occasional dodgy sensors and the fact that newly activated sensors tend to be inaccurate for the first 24 hours.
Maybe
@Senior_Squirrel has already done this, but I would strongly recommend any new user to do a large number of blood tests to compare the libre reading with the corresponding blood glucose level to work out how reliable a system it is for him/her. It works very very well for many people, until it doesn't. I don't personally think that it can ever completely replace traditional blood tests, though I believe it can come close if you are compatible to it and you add in the software to calibrate it against your own personal blood tests (which means you'll be doing calibration tests if nothing else).
Though I'm sure it must be very frustrating if you've already taken sugar to increase your levels and you know they are going up, the consequences of going hypo while driving are so catastrophic that it's probably best to have a traditional blood testing kit in the car to supplement the libre, just so that you can be sure you are safe. (Speaking from personal experience of my one driving hypo a couple of decades ago which did not but easily could have ended in disaster.)