No there is not an injection to cancel the depo injection you have o wait out the whole 12 weeks.After the injection wheres off it may take up to 12 months even loger for your menstrual cycle to come...
Im on the depo injection i had my 4th one in December and about a week later i came on my period and iv been on it now for over a month even though i havent stopped taking the injcetion im still on...
Hopefully, you will not conceive while you are on depo, since it is a drug that you should not have while pregnant since it may cause birth defects. Wait until you have a good home situation before...