When I light my oven, it stays on full all the time. Is it the thermostate

I'd recommend buying an oven temp dial to stick in your oven to verify the actual temp. Then you can turn on the oven using a lower setting and write down the temp for the setting. Then as you slowly adjust the setting higher and higher, note each temp. If it doesn't show a consistent increase of temp for each setting, you may need it calibrated or replaced. Good luck!