I had this only last year. Weird sensation in my bits and feeling pretty grotty. Went to doc and the urine test showed traces of blood.
Blood test AOK and Ultasound clear - 1 x course of antibiotics and all gone.
My dad has just had bladder cancer and that started with an eruption of blood all over the bathroom from his JT - a bit like Custer's Last Stand. Straight into A&E and admission to Urology. Even then, one quick operation to remove growth and all cleared - nothing shown back up at all.
As already said, don't panic and don't let your imagination run riot. It'll probably turn out to be OK. If they were really worried, they would have had you in for tests stat.