Congratulations on the weight loss!
About blood test machines - In order to comply with ISO standards, blood glucose monitors just have to be accurate to 15% . There are also lots of other factors which can make each reading slightly different (the number of red blood cells in each sample size, trace substances on your hands). The general consensus is that these monitors are designed to give a good guideline of where your blood sugar is at, but won't ever be 100% accurate, and won't be as precise as a laboratory test.
We've all been there with the testing and re-testing, but eventually you do come to a point where just one test is enough! If for no other reason than the finger callouses get annoying.