It has blamed a calculation error.
Suicide bombers struck hotels and churches in the Colombo area and the eastern city of Batticaloa. Hundreds were injured, officials said.
Most of those killed were Sri Lankans, but dozens of foreigners were also casualties. Nine people are suspected of carrying out the attacks.
Police have continued carrying out raids and have issued photographs of seven people wanted in connection with the attacks.
The authorities blamed a local Islamist extremist group, National Thowheed Jamath (NTJ), soon after the blasts but say the bombers must have had outside help.
The Islamic State group said it was behind the attacks and published a video showing eight men but provided no evidence of direct involvement.
In other developments:
- Hundreds of Muslims, fearing revenge attacks, have been fleeing the city of Negombo, site of one of the attacks
- Sri Lanka's defence secretary, Hemasiri Fernando, the top non-elected official at the department, announced his resignation on Thursday in response to intelligence failures
- The country's Catholic Church has announced the suspension of all church services
- Police say more than 70 people have now been arrested
Why was the wrong toll given?
Sri Lankan Deputy Defence Minister Ruwan Wijewardene said morgues had provided inaccurate figures.
Another official, the head of health services, told Reuters news agency there had been so many body parts it was "difficult to give a precise figure".
According to the health ministry, all autopsies had been completed late on Thursday and it transpired that some victims had been counted more than once.
BBC World Service South Asia editor Jill McGivering says the revised figure comes as the government is struggling to restore its credibility - amid criticism of its apparent failure to respond to intelligence warnings before the attacks.
It's also battling to counter fake news and false rumours about the crisis, she says. This sudden dramatic revision is unlikely to help.
What is the situation with the Muslim minority?
Muslims in Sri Lanka are reporting feeling fearful and say they are facing persecution.
Many of those in Negombo belong to a minority sect, the Ahmadi. Some have been sheltering in a mosque under police protection.
Ahmadi Muslims identify as Muslim and follow the Koran, but are viewed by many orthodox Muslims as heretical.
Many of those living in Sri Lanka have fled from persecution elsewhere, including Pakistan.
The Prime Minister, Ranil Wickremesinghe, has admitted that some Ahmadi have been subject to attacks. Of Sri Lanka's 21-million population, just under 10% are Muslims.
A community in fear
Muralitharan Kasiviswanathan, BBC Tamil, Negombo
As of Wednesday, more than 600 Ahmadis had taken refuge at Faizul Mosque in Negombo, one of the five Ahmadi mosques in Sri Lanka.
Most of the Ahmadis were renting their homes from Catholic Christians. Although the bomb blasts happened on 21 April, it was on the 24th that things got scary for the Ahmadis.
"My home is some streets away from the church. After the attack, the owner of my house was very worried and asked me to be safe somewhere. I am paying 13,000 rupees [£58; $74] for that house. Most of us paid a year's rent an advance. Where will we go now?" asks 27-year-old Habis Rabba Soaib.
About 800 Ahmadis from Pakistan live here with the help of the UN refugee agency, UNHCR. Fearing religious prosecution, they fled Pakistan and came to Negombo. From here they seek asylum in European countries or the US.
Although the Faizul mosque is small, officials of the mosque are taking care of them and sending most of them to another mosque, Pesalay, which is in a safer location. This mosque is now guarded by army and the police.
More than 5,000 native Ahmadis live in Negombo. Many of them have lived here for years and now own houses and businesses.
"Since we are here for a long time, nobody is threatening us," says one of the Muslim youths who is busy helping the Pakistanis.