On the assumption you washed your hands before the blood test, then I would suggest you go by the blood test rather than the Libre
Regarding the difference between the results of the two blood tests, there are often differences when at either more extreme end of the range so I wouldn't be too concerned regarding the difference between 8.4 and 8.0. Also, a different test strip may give a slightly different result. Different meters can often show slight differences.
As for the Libre being so low, there is a time lag before the Libre catches up with the blood test, particularly if it's changing fast. If the Libre is continiously well out of kilt with blood tests, then contact Abbott during the week