You're effectively trying to run a 5k here before you've even learned how to walk. As others have said, start with a simpler problem or just hold off until you've taken the FEM course at your school. If you want a jumpstart on learning some concepts, look up stress singularities. That ought to help you understand why your stresses don't converge and only shoot up towards infinity. Also, whenever you're looking at high stresses in very small areas, it's a good idea to display the mesh on the result plot so you can see if your results are mesh dependent and to see if you're dealing with a stress singularity or a "real" stress. Finally, doing a hand calc like you've already done is good practice. You should pretty much always do a hand calc so you know what ballpark your results should be in (this helps detect large issues in your model setup).