Since you were still fertile, about 20% which is as good as it gets.
It's too early to test. You need to wait AT LEAST two weeks or until your period is due. Even then may be too early. The tests are only really accurate when they show "pregnant."
False negatives are VERY common - more so testing early. False positives are very rare.
Even the "early tests" are unreliable. It's all just advertising.