how long did you break the engine in for ?
shavings may not be the issue , one or more of the gears on the main shaft may be galled or seized , that is why the car tried to move on you , that is a massive oooopppp s
I would not pull the cover , not easy to install again in the car , add oil to the trans & see what happens , I think you will have to pull the trans as 1 or more of the gears on the mainshaft & possibly the main shaft may be damaged now