Accuracy of do it yourself radon tests.?

My husband and I purchased a new construction home last year. The builder offered to install a radon mitigation system in the home if we tested for radon within 30 days of purchase. Stupidly, we got distracted and never did the radon test on the house.

In talking to several neighbors (one who lives behind us, the other two doors down) we discovered that they did radon tests and the radon levels in their home was really high.

We quickly ran out and purchased a test from Home Depot. I received the results back today and the levels were low, 2.7 and 3.1 for each canister respectively. How accurate are these tests? Can radon be high in one house and literally next door, there is very little radon?

Just wondering if I should retest. We would like to get the basement done and I want to make sure we don't need they system installed.

Thanks!