I can understand the concern you have,but as you said yourself, your not sure you even had a risk. That said, you are certainly negative and your 26 week test is as good as you can get. Delayed sero dosnt really happen, its very very rare indeed. It was possible for people to test postive after 3 months, but with modern tests and a better understanding of hiv it just dose not happen.
You can relax, you dont have hiv