As @tristan said, with about 7000 previous investors, even if you presume they all invested at £1000 (and they won’t, lots of folks invest closer to just the minimum of £10, or around £100) that’d still be only £7m of the £20m target.
Anyone who wishes to invest, provided they do it earlier rather than later, should be able to invest as much as they are able to, up to the £2000 limit. It’s quite unlikely that anyone will be left behind, unless they simply miss the announcement and miss the whole thing.