If you ended up coming to Cambridge with erg scores like that, and under 2 years of rowing experience, I would personally be recommending you to row for your college in your first year (unless your college is one of the less established clubs on the river). Ergs don't float and all that - so it's hard to say just how good you actually are. But I would guess that you would be capable of being in your college's first boat almost certainly (especially with past rowing experience). If you were a bit of a spacker on the water though then you might end up slipping in to the second boat, but you'd have to judge your ability for yourself.
The reason I say don't trial in your first year is because it does take up your life - which is arguably better spent getting to know your peers. You're certainly not of the standard to make a competitive shot at CUBC if you ask me. You would probably need to join the CUBC year long development squad, and work your way in to the club by that route (which involves you rowing for your college anyway).
As for CULRC, although it's much more accessible to non-olympic rowers, you would have to judge for yourself whether or not you have the weight to lose to get down to the required weight range. But again, you should leave that until at least your second year.