The problem with that is...it is only a 48 hr test. Your minor problem you think you have changes daily. I have been involved with radon testing and training for 15 years...before it was the norm. To get a real valid test you need a real long test to mimic winter conditions. Just install a system to get rid of the gas, then when you sell there is no more issue. Systems cost about 600 to 1500, and you can even run the pipe yourself. Then the radon company is responsible for getting the ##s down.
Plasyic on the floor is a start, but the gas still escapes from under the plastic. Imagine a balloon with a hole...without a continuously running fan, it will all leak out....meanwhile your lungs are the filter.
Good luck with your decision.