Verifying Tensile Test on Sheet Steel

Hey guys,

Okay so next week I'll be preforming a tensile test on SS304 sheet metal dogbone specimen and currently I'm doing a FEA to determine what results are likely to be seen. I'm only analysing the elastic region.  Now I've done some hand calculations aswell, with the hope that I run FEA at various levels, record the stress strain and displacement and then compare to hand calculations.

Now straight off the mark they are not similar, theres about 0.05 mm difference between them! Any idea why? I've used same Young's Modulus for both. Is it that Solidworks is taking into account variables which arent assumed in basic hand calcs?

This is when i add fixture and loads to the pieace on top and bottom. Now realistically I should be using split contacts and gripping it on the sides. However when I do this I get crazy high stress values at loads where it shouldnt be beyond yield but it is.Any ideas on this too?

I attached some pics if anyone can help I'd be really greatful.

SolidworksSimulation