Hi Ian,
Where Eta Carina lies, there is an enourmous star cluster (NGC 3532) smack bang between it and the Southern Cross, and it would have been right in the line of sight that you were mentioning.
It is VERY easy to confuse 3532 at first with Eta Carina. I've done it, and STILL do, thirty years on. Both Eta Carina and 3532 are just visible to the naked eye from urban areas. The trick is, once you've spoted something you believe to be Eta Carina, and you see no nebulosity (like you mentioned you hadn't!), you are not in the right place. You will need to keep paning the scope a little more to the west.
I've attached a sketch I made of Eta Carina through my 8" f/4 dob at 29X. I did it while the Moon was at first quarter too, much like it will be appearing now with the Moon up. If you didn't see this, it isn't your scope, you had just missed by
1 width of your field of view to the west - just missed, in other words,
.
To make matters a little more interesting, there is a second giant and really bright cluster just to the south of Eta, only a little further away from it than 3532 is, and is as bright to the naked eye as both Eta and 3532. IT TOO will get you!
. It's tell tale sign is the component stars are much brighter, fewer in number and much more widely space.
Your scope is a very good instrument. Once you've pinned Eta, you'll definetly know you've got the Real McCoy!
Like Ibrahim said too, the near full Moon doesn't help. And while a nebula filter does help, Eta Carina is still bright enough that you won't need a filter to make out its details.
I'm sure you'll pin it tonight with this info on board. Yet us know how you go.
One last thing, I don't know how much experience you've got with scopes, so I'm sorry if you already know not to expect to see the lovely pretty colours that we all see in photos of the sky. It doesn't work that way with our human eyes. Like I said, I don't know your experience, so I can't make the asumption that you already knew that. It's because you mentioned that you were disappointed that the image in your eyepiece didn't match what you saw in a photo. It never will. Have a lot through the Solar System and DSO Sketching sticky, it will contains many sketched examples of how you will see things through the eyepiece and so what to expect.
Mental.