I would advise you see a vet right away. Especially if you think it is an infection or a tumor.
Until then, you can use one of these home-remedies that will help:
1) "you can make a home antibiotic using fresh thyme (the herb). boil some water, and pour it into a mug containing a good handful of fresh thyme sprigs. let this sit for at least 15 minutes, stirring occasionally. then, you can use a paper towel to filter the thyme-infused water from the sprigs.
use this thyme water to clean your hedgehog's cut, 2X a day." - missPixy from Hamster Hideout
2) Make a batch of Epsom-salt-water with 1 part water and 1 part epsom salt. Use warm (not hot) water, and natural Epsom salt. Soak a washcloth in this solution and gently dab it on the infection. It will draw the infection out and keep the wound clean. Do 2x daily.