Is a negative digital clear blue pregnancy test pretty accurate 26 days after sex and 4 days after a missed period?

The hormones created by pregnancy should turn a urine pregnancy test positive 2-3 weeks after exposure or at the point menses is delayed by pregnancy. False negatives do occur. Testing on a first morning urine is likely the most concentrated & most representative of a true test.

What you described suggests that you are not pregnant. If you have any doubt you may repeat the test with first morning urine in 4-5 days. Alternatively you could get a blood test for HCG now to settle the issue. Wish you good health!