The Games are due to take place between July 7 and 20 but the country was only confirmed as host in December 2017.
Apia stepped in following the withdrawal of Tonga who cited financial concerns.
It means Samoan organisers have had a shorter time than usual to prepare for the quadrennial event.
"Friday marks 100 days until the Opening Ceremony of the Samoa 2019 Pacific Games, and to say that it has been a hectic year of preparations would be an understatement," said Matatia.
"Over the past six months, the region has witnessed an outpouring of support from both our public and private sector who have left no stone unturned to help Samoa put its best foot forward.
"Leadership is what has enabled us to get to where we are today."
Matatia added: "We are blessed with exceptional and strategic leaders within both our Executive and Organising Committees.
"They are supported by teams working tirelessly to put into action solutions to ensure our Games are a success and provide a legacy for our people.
"We wish you all the best in your preparations towards the Games and ask that you keep our humble nation in your prayers as we work to make history."
The recruitment of 11 sponsors has particularly been highlighted as a major plus point for organisers.
Backers come from the private and public sectors, as well as state-owned organisations.
It has led to Samoa 2019 being described as "the miracle Games" by director of sponsorship Tagaloa Fouina Su'a.
A total of 26 sports are set to be contested at Apia 2019.