Barrons's Practice Tests/SAT II Lit and Math Questions

I am planning on taking the Math level 1 and Literature SAT Subject Tests on June 6th. I bought Barron’s to help me study for it since that brand was such a huge help studying for AP World last year; however, I am getting very nervous because I am doing extremely poorly on the practice tests. I’ve been scoring low 600s for both of them. I read somewhere that Barron’s tests are much harder & that the really tests, in comparison, are a piece of cake. How much truth is there to this? I know I won’t be getting an 800 on either but I’d at least like to get a high 600 on both of them. Are the subject tests similar at all to the math and cr section of the SAT? Thanks for the help, and I’d appreciate and input or experience anyone has with these books or tests!!

On the actual sat, I got a 720 in math and a 670 in Critical reading, if that matters at all.