I have been in the UK from the US under a Tier 4 visa for 6 years (3 years undergrad, 3 years postgraduate research). I recently completed my last degree, and my visa expires December 31st of this year.
Meanwhile, I have been with my boyfriend (UK citizen) the last three years. He proposed at Christmas, and we want o give notice to marry.
I know I have a 28 day grace period to either put in another application or get my stuff together to go, so effectively, I need to have things sorted by January 28th. I realise there is a 28-day notice period for marriage so even if we give notice this week, assuming everything could be done quickly it is still cutting it tight. Would it look bad if I submitted an application January 27th for a spouse visa? We would have everything we need - appropriate paperwork (we've been living together for nearly two years and the house is in both our names' which should help) and he is on an appropriate salary to support us as per the guidelines.
And assuming things do not move quickly, despite giving notice, Will I still have to leave by January 28th or is it better to stay and apply on a fiancee visa?
I think I am just worried if I did have to go back to the states and come back because I am even more confused as to what I would need to do to come back to the UK to actually get married without being denied entry. I think watching "UK Border Force" has me paranoid

Sorry for the long post! I hope it is enough information. Thank you!