passport visa citizenship travel kerfuffle

Hey guys,
I think I'm about to land myself in a world of trouble travelling.

I received my UK citizenship in January (yay) but since then haven't gotten around to getting my British passport. I recently booked a last minute trip to Amsterdam with a friend and now realise that I don't think I use my US passport to get back into the UK. My US passport still has the unlimited leave to remain visa in it but I'm assuming that's cancelled now I'm a citizen even though there no indication in the passport that its invalid. I'm planning on bringing my citizen document and some other paperwork that says "yes I belong here" but I'm worried that customs will be unreasonable. I know I Should have gotten a UK passport but I feel like I should still be able to travel as an american. 

Any ideas? Am I screwed?

I don't think you are screwed.  Yes, there may be a few more questions than usual at the border, but shouldn't be too bad.

I got my citizenship a few years ago, just before moving back to the US, so there was no big rush for me to apply for a passport.  I still don't have a UK passport and I have travelled back several times (albeit as a visitor) without any problem.  The last time I travelled back the IO told me that my ILR was still valid even though I had citizenship. 

I would still bring all your docs with you, just in case and explain that you weren't able to apply for a passport in time if asked.

Thanks Karin, that's a load off my mind!  Its hard to find any info on this anywhere.

I got my citizenship almost 2 years ago, and I've been in and out on my ILR several times since then.  Just don't mention it.  There's no requirement to enter the UK on a UK passport, and your ILR is still valid.  No worries.  It does mean you have to go through the non-UK/EU line, but that's not usually a big deal.