Apologies, what exactly do these bill entails. I don't fully understand bills and acts and such. What was in that bill? And by not "cutting back", what does that imply?
An act of parliament is known as a Bill until it is passed by parliament, then it becomes an Act (strictly, when it receives royal assent, but that's just a formality - the last time royal assent was denied was 300 years ago). An Act is a law.
The King's Speech is written by the government to say what bills they will bring forward over the new session of parliament (a year or so).
There was an act of parliament to authorise the construction of HS2 phase 1 (Euston to Birmingham and Handsacre) and another to authorise phase 2a (Handsacre, or strictly speaking Fradley, to just south of Crewe).
There was a bill for phase 2b which originally covered from just south of Crewe to Golborne (just south of Wigan) with a turnoff to Manchester Piccadilly. First the Golborne link was deleted a few years ago, leaving Crewe to Manchester.
Then last year Sunak cancelled phase 2a and part of 2b, leaving just the part nearest Manchester, because that also forms part of NPR.
The outgoing government was proposing to delete the southern part of phase 2b from the bill, but I can't remember whether they got as far as doing so before parliament was dissolved for the general election.
If I remember correctly, the north-eastern arm of HS2, from east of Birmingham to Leeds and Church Fenton, later cut back to East Midlands Parkway, never even got as far as having a Bill published.