Figen Murray hailed the support at a vigil celebrating the 29 year old's life in Heaton Moor Park in Stockport, Greater Manchester, on Sunday.
Mr Hett was one of 22 people killed in the suicide bomb attack on 22 May.
Mrs Murray said his friends were "all very tearful and yet they said the most beautiful things about him".
A Coronation Street-themed cake was among the tributes at the vigil for Mr Hett, who had a tattoo of the soap's stalwart Deirdre Barlow.
Members of his family also wore personalised T-shirts with tributes from celebrities including singer Mariah Carey and BBC Radio 1's Nick Grimshaw.
Speaking in front of hundreds of people who attended the vigil, Mrs Murray said: "I know I've lost a son to this horrible event but they were his friends before and I've gained more sons now."
She also spoke about a hashtag #BeMoreMartyn which was being used to pay tribute to Mr Hett on social media.
"I don't know how that came about and who started it but I'm going to have it tattooed somewhere on my body. I think he's taught us all a lesson how to live life more fully," Mrs Murray said.
Mr Hett's partner Russell also paid an emotional tribute to the "Deirdre to my Ken" on stage at the vigil.
"I feel robbed of my future, but I feel so grateful of my past", he added.
Mr Hett died just days before he was due to fly to the USA for a two-month "trip of a lifetime" for which he had been saving for two years.

Eighty-five per cent of all births in Brazilian private hospitals are caesareans and in public hospitals the figure is 45%.
The new rules oblige doctors to inform women about the risks and ask them to sign a consent form before performing a caesarean.
Doctors will also have to justify why a caesarean was necessary.
They will have to fill in a complete record of how the labour and birth developed and explain their actions.
Each pregnant woman will now be assigned medical notes which record the history of her pregnancy, which she can take with her if she changes doctors.
The new rules are designed to reduce unnecessary surgical procedures, and ensure pregnant women are aware of the risks associated with caesareans.
However, experts say that a scarcity of maternity beds and wards equipped to deal with natural births means that for many women in Brazil, caesarean birth is seen as the best option.
"The best way to guarantee yourself a bed in a good hospital is to book a caesarean," Pedro Octavio de Britto Pereira, an obstetrician and professor at the Federal University of Rio de Janeiro, said in an interview with BBC Brasil last year.
Women who want to give birth naturally in a private hospital have reported finding all the beds are reserved for scheduled deliveries.
There have been numerous reports of women going into labour without a caesarean scheduled and being forced to travel from hospital to hospital in search of a bed.
Researchers say many women also see caesareans as more civilised and modern, and natural birth as primitive, ugly and inconvenient.
In Brazil's body-conscious culture, where there is little information given about childbirth, there is also huge concern that  natural birth can make women sexually unattractive.
Many doctors prefer caesareans too, as they can plan the time of a birth, and feel more protected from litigation.
Gynaecologist Renato Sa told BBC Brasil: "Doctors are responsible for what happens and in a situation of risk they chose a caesarean, because if there is a death or complication they will be asked why they didn't do this. Doctors are afraid of natural childbirth."
The mother of Manchester attack victim Martyn Hett says she feels she has "gained more sons" thanks to the support of his friends.
[NEXT_CONCEPT]
New rules have come into force in Brazil aimed at reducing the country's high number of caesarean births.