@Ktmc94 YANBU to be a bit pissed off and feel irked. You are entitled to feel this way. And I think you're being given a hard time on here.
However, I think it's a good idea to have a smear test. They save 10s of 1000s of lives a year, and are quite painless. Sometimes a bit uncomfortable, but not painful, usually.
And the nurse did sound a bit brusque! I have encountered a few brusque and abrupt nurses, but most of them are lovely. Even the abrupt ones are still good. They are just a bit 'no-nonsense!' And you ended up feeling a bit 'small.'
Don't take it to heart, and please don't dwell on it, and I can't see any point in reporting her, because you will be told she did nothing wrong. They won't care that you were embarrassed and felt awkward, and will say (like some posters on here,) that you should be grateful for the FREE healthcare! And I agree it's a bit out of order to be bullied into a cervical smear when you are just going there regarding your contraceptive pill!
Have to say though, I've never heard of a larger speculum being used coz someone is 'fat!'
That's a new one on me.
It's horrible when you feel like you have been railroaded into something you didn't want to do, or weren't sure about... But don't let it get to you. I have had similar things happen in the past, and although they often mean well, it has pissed me off.
Several times before, I have been hounded into a medicine review by a pharmacy. 'Just 2 minutes it will take' they claim. ALWAYS takes 20 minutes minimum, and they ask so many questions. I see the doctor regularly, and don't need a bastard medicine review at the pharmacy. Moreover, I know they get paid for every one they do. So they are only doing it for the money, and not because they care about you and what meds you're taking! (In my opinion!)
And they are meant to give out advice on weight, but I have no idea why the nurse lectured you at your smear test. And when your weight is mentioned, it can sting a bit sometimes.
I have found they can come across as inconsistent too sometimes. For example, several years ago, one nurse told me I needed to lose weight, (at least a stone and a half,) and a nurse several weeks later, told me I was fine, and 'didn't need to worry.' I was about 2 stone over my 'ideal' weight at the time... So that made me a bit 
All the best. Hope you are OK 