The risks of not going ahead with the project "significantly outweigh the risks of doing so," added the report from the House of Commons Transport Committee.
The committee, chaired by Louise Ellman, Labour MP for Liverpool Riverside, also said serious thought should be given to building the second-phase northern section of the line at the same time as the London-to-Birmingham phase.
The committee said it remained "convinced that the project is justified" but added they would not accept other vital transport projects were delayed due to HS2.
The cost of the project in its entirety is estimated at £42.6 billion with £7.5bn needed for the high-speed trains. Of this £42.6bn, a total of £14.56bn is contingency.
A study aiming to increase the benefits to Scotland of the HS2 rail project was announced by the UK government last month.
In its report, the committee said: "The Department for Transport's (DfT's) communications about HS2 should emphasise that the estimated cost is £28bn, not £50bn, and that cost increases to date have largely been due to the decision to undertake more tunnelling and other work to mitigate the impact of the project on people living near the route."
Joe Rukin, campaign manager for the Stop HS2 group, said: "Despite the official cost of HS2 standing at £50bn, the committee want to pretend it is £28bn, even though they said it would be £34bn in 2011.
Transport Secretary Patrick McLoughlin said: "HS2 will be a heart bypass for the clogged arteries of our transport system. We therefore welcome the Transport Committee's conclusion that the new North-South railway is the best long-term solution to increasing capacity and that alternative proposals would simply not cope with the predicted increase in demand."