Theresa May was warned by a senior party strategist that her gamble of calling a snap general election carried "a lot of risk", according to a leaked memo.
The note, written in April, just days before Mrs May announced her surprise decision, said voters did not want the uncertainty an election would cause.
It warned there was a risk the Tory vote share would end up "broadly similar" to that achieved by David Cameron in 2015 when he won a narrow victory, rather than the landslide sought by Mrs May.
When told about the plan to call the June 8 election by Tory campaign chief Lord Gilbert, campaign guru Sir Lynton Crosby reportedly responded by saying: "I'm not sure that's a smart idea, mate."
The leaked "Election Strategic Note - April 2017" memo was obtained by the Mail on Sunday.
Drawing on focus group research and national polls, it opened by warning "there is clearly a lot of risk involved with holding an early election - and there is a real need to nail down the 'why' for doing so now".
Voters were "actively seeking to avoid uncertainty and maintain the status quo, and yet by calling an election the Conservatives are the ones who are creating uncertainty", it continued.
It warned that Mrs May's strong opinion poll leads at the time meant there were "exceptionally high expectations" she would be returned to Number 10 "leading voters to believe that they can vote for the best local MP while still remaining secure in the knowledge that Jeremy Corbyn will not be PM". But it also said voters were worried about the risk of a hung Parliament creating "chaos over the delivery of Brexit".
Mrs May lost her Commons majority after calling the election and has been forced to rely on a pact with the DUP to bolster her position in Parliament.
She used a trip to Japan last week to insist she would stay on as leader and fight the next general election - telling reporters she was "not a quitter" - but opinion polls suggested she should go if the Tories want to remain in office.
A Survation poll for the Mail on Sunday put Labour on 43%, a five-point lead over the Tories on 38%. Some 42% of voters said it was "unthinkable" Mrs May will fight the next election - including 39% of Tory supporters - and Mr Corbyn was backed by 40% to win the next election, one point ahead of the Prime Minister.
Brexit Secretary David Davis told BBC One's Andrew Marr Show yesterday that Mrs May was a "great Prime Minister".
Asked "did your heart lift" when Mrs May said she would stay on, Mr Davis said: "I have served her for the last 12 months, I have been never anything less than impressed with the way she runs the country.
"That's what matters to the people - not the politics - running the country and she has done a good job."
Trade Minister Greg Hands noted that "five years is a long time in politics" but the Prime Minister was doing a "fantastic job".
He added: "I'm expecting it to be a five-year parliament, and five years is a long time in politics.
"I think the Prime Minister is doing, at the moment, a fantastic job - it's a very, very big job at the moment - a lot going on domestically, the Brexit negotiations."