I don't know if this will help you at all thagerty, but I just finished taking the HESI and had to take bio, chem, grammar, vocab, math, and reading.
I felt like the chem was very, very, very basic. If you know and understand the concepts presented in the study guide and you did well in your chemistry class, then you should be fine - I ended up getting a 96% on the chem portion and only skimmed over the chemistry part a couple times and took the practice exam, in my opinion everything you need to do well on the chemistry part is in the study guide!
Now, I do have to agree with the others who have said that the bio portion in the study guide is not sufficient, or at least it wasn't sufficient enough for the bio portion on my test. I ended up getting an 80% which was my lowest score - and I am really good at biology.
I would definitely look over old notes, textbooks, etc. for the bio portion. If you can, a quick A&P review may help you also if you have already taken it, if not, I would suggest reading the A&P section in the study guide - I feel like if I had done that my score would have been higher! I supplemented the biology portion of the evolve study guide with the McGraw-Hill study guide, and my old textbook, and I still did not do as well as I was aiming for.
Don't stress yourself out over the HESI, I got no sleep the night before because I was so stressed out about taking it, and ended up getting a cumulative score of 90.67% and walked out happy!