Gasket around rim of oven broke while cleaning

Son-in-law unscrewed oven compartment; broken gasket was easy enough to remove and new gasket easy to replace; only problem was oven door would not shut tight. Tried shoving gasket harder into groove, tried turning on oven and heating new gasket to see if it would soften. Finally got it to close by pushing hard on left side of oven and inside light would at least go off and stay off.