David Rawcliffe, 29, from Blackburn, inappropriately touched the victim on several occasions between 2016 and 2018, before being reported to the police.
After being questioned by officers, Rawcliffe admitted to the offences described by the young victim, some of which took place when she was only 13-years-old.
On February 14, at Preston Crown Court, Rawcliffe pleaded guilty to eight counts of sexual activity with a child and one count of engaging in sexual activity while in the presence of a child.
He was sentenced to two years and four months in prison.
But after being reviewed by the country's top lawyer, Attorney General Geoffrey Cox QC MP, the sentence was considered unduly lenient and was referred to the Court of Appeals.
At the appeal hearing, Rawcliffe's sentence was increased by 12 months, meaning he will now serve three years and four months in prison.
Speaking after the hearing the Attorney General said: “The offender’s actions have had a severe impact on the victim and I feel the increased sentence more accurately reflects this.”
Rawcliffe was also made the subject of a sexual harm prevention order, and has been placed on the sex offenders' register for the next 10 years.