What do I do if there is blood in my urine ?

Need evaluation. Having any amount of blood in the urine needs to be evaluated by a urologist whether the bleeding is microscopic or can be visibly seen in the urine. There are many causes to having blood in the urine which maybe from benign or malignant causes depending on your age and other risk factors such as smoking.
Get checked. Depending on age and other factors, this can be caused by several things from infection, to a mass, and many others. I would suggest getting checked out by your doctor and possible urology.