You will be fine. There's actually a buffer in there for this reason. Depo takes a long time to get out of your body. If you're getting your shots on time then you don't have to worry about ever being unprotected

Eiri is right I was on the shot for 3 years and never once worried...the dr told me to use extra protection if I missed my appointment and was a few weeks late for it but that happened once and she said she doubted anything would happen but just to be safe so you are totally fine as long you keep on schedule

also, i was wondering what are the effects if you drink alcohol while on the depo shot? i just got mine last week, i am average size and am terrified of gaining weight.