How far off is the temp? Even new thermastats need calibrated

What sort of instrument were you using to check the temp? The reason I ask is I get lots of people using cheap oven analog thermastats they stick on the rack that was bought at walmart and they are never accurate .One needs to use a digital thermometer with type J or K thermacouple to accurately test oven temps Which are usually Found in a good Multimeter type or one specifacaly designed to handle high temps.

Most of the time there is an adjustment screw in the shaft of the thermastat which just a minor tweek will take care of it but to set it accurately hyou need a good temp probe so you can tell where you're at with temps most of the time you can get 50 degrees out of the adjustment or if you're the kinda person that isn't picky set your control to 400 and pretend it's baking at 350

Sounds like the pilot lite went out

did you try it again? the pilot assemblys get carboned up I would turn off gas remove assembly and clean it and clean the pilot generator you can clean it as well by leaving it in get a small wire brush and shine it up sometimes thats all it takes Those gas valves are pretty bullet proof and seldom fail but I suppose the safety in it could be bad but I have repaired many gas stoves that acted like a gas valve and just the pilot assy was needing cleaned