You can get a oven thermometer to check and see how off you are, they are cheap under $10. If you aren't too far off then you can easily adjust your temps when turning on the oven.
If it is way off, it can probably be repaired or calibrated. But, as has already been mentioned, this might be a good excuse to shop for a new stove. In my case, I had the coolest 1965 stove in my house (same frigidaire stove as in the old Bewitched show, google it!) and it worked great. But we remodeled and I decided I wanted to go more modern with my appliances. Its amazing how much the power useage dropped with a new fridge and stove in my all electric house.