Last week the 23-year-old agreed a new three-and-a-half year deal with the Gunners, ending another long-running contact saga and months of speculation linking him with moves to Chelsea, Manchester City and Liverpool.
Walcott has impressed this season, top-scoring for Arsenal with 15 goals in 27 appearances, but has conceded that the drawn-out talks over his future affected his concentration on the pitch.
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"For the last three games [before the Chelsea match] it was sort of done but it was on my mind and had been for a long time because it was so close.
"I always wanted to stay and I am happy that myself and the club have come to an agreement.
"There has been much speculation and I am very pleased that my future is sorted. But it is all about the present now."
Walcott scored Arsenal's only goal in their 2-1 defeat away to Chelsea on Sunday, just 48 hours after the club confirmed that he would be staying.
The Gunners face another London rival in the form of West Ham at home on Wednesday evening, and Walcott believes it is a game they desperately need to win if they are to remain in the hunt for a top-four place.
"We have a tough game at home against West Ham, so we need to be ready," he continued.
"It is a massive game. We have home support and we need to start clocking up points there.
"There are a lot of teams that have got stronger this year, so we need to step on the gas. We don't want to be playing catch-up.
"We want to get points on the board."