The given mechanical property "elongation" is normally @ break.
To calculate Young's Modulus you need to know this value @ yield.
But as you mention, steel is steel, and you can generally use a value between 205±5 GPa as E-modulus.
If we calculate in reverse, 305 MPa / 200 000 MPa => 15% elongation @ yield.
Realistically, you only need Young's Modulus and Poisson's Ratio (and density) for FEA but SW also wants YS/TS for the FoS.
Use published values for steel.
Did you happen to notice that on the website you cited that it lists the MoE, Poisson's Ratio and density?