Maddison has six caps for the national team but has never played a full 90 minutes. Despite being named in the squad, Maddison was sidelined with a knee injury during the 2022 World Cup in Qatar.
He did not feature in England's 1-0 defeat to Brazil in the international friendlies but came on as a substitute in the 74th minute against Belgium on Tuesday.
Maddison delivered a swift low cross to Jude Bellingham, who netted the goal in the 95th minute to rescue a 2-2 draw with Belgium at Wembley.
"There is big competition, a lot of quality in the squad. I know the quality that I possess that can help this team," Maddison said of his prospects on Wednesday.
"I don't lack the confidence and belief in myself to do that, you have to produce. Against Belgium, I came on and made an impact. I'm showing him (Southgate) what I'm capable of and I just want to show more of that."
England are grouped with Slovenia, Denmark and Serbia at Euro 2024, which begins on June 14.
