There is no risk with a handjob, and a single small red bump isn't a symptom of any STD.
If you experience another bloody ejaculation, please be seen. There are lots of causes for that, and STDs are way down the list, but all need to be addressed.
The risk of handjob js negligible. However, certain stds can be spread through contact with sores.
It would be a good idea for u to go and consult a doctor.
Tell the doctor your symptoms, and do the appropriate tests.