Should I turn down imperial college london to try undergrad application in US again? (Would mean a gap year)

What’s the course at Imperial? If there’s an option for an industrial placement, there are generally some options which are either US based or can lead to US placement for return offers. These are obviously tech jobs, Silicon Valley generally, rather than finance, though occasionally people do go directly to NYC for quant funds (I certainly wouldn’t count on this though). 

From a recruiting/opportunities perspective, only HYPSMW are going to give you a significant leg up in the US compared to what Imperial offers in Europe, which is broadly equivalent to a Columbia/Chicago/Duke/Cornell/etc tier. And the chance of you getting any of HYPSMW are probably quite slim on a second attempt... unless you *really* want to be in the US for your analyst years (you can always transfer from London later), it doesn’t make sense opportunities wise to reject Imperial and reapply to US universities to only get into a T20 school. 

Now what you haven’t said is what you actually want out of uni. Imperial is quite unique, and not necessarily in a good way - workloads across the overall university tend to be the highest in the U.K. (although less compressed than Oxbridge’s eight week terms) and it’s a bit of a sink or swim environment and not especially academically collaborative (less so than tech places like MIT in the US). From a ‘college experience’ perspective, most US T20 schools (CalTech and Berkeley aside, perhaps) are going to be more fun than Imperial, as are most U.K. schools. That said, Imperial’s societies are excellent and the whole uni is a lot less cliquey/more open than Oxford/Cambridge/LSE. You’re also in one of the nicest areas of London, which depending on both your tastes and your wallet, can be a great place to be a student (though I’ve got a lot of friends who prefer Oxford/Cambridge/Durham/St Andrews type student towns).