Hi and welcome to HCM. Thank you for your query.
It lookl like there is subcutaneous hematoma
. This is nothing serious. This is just blood accumulation beneath the skin and it will pull back in short time.You can apply some heparine gel if you have,keep your hand elevated and keep it clean to prevent infections. If you notice pain, tingling
or paleness of hand and fingers,you should visit doctor as soon as you can. Regards