Thats kind of strange. Under system properties that should have been your actual Memory and not what is available. Well anyway it looks like you have most of your memory.
Did it say 2.75 available or total? It will never say 3GB available because it will have to use some of that to run your base OS. Since your system doesn't see past 3GB the extra 1GB basically has no use and will not show any difference in your available memory or total memory. If it says you have 2.75GB available then you are absolutely fine.