Costa made his Spain debut in a 1-0 friendly victory against Italy in March last year but did not open his account for the European champions until his seventh, and most recent, appearance, a 4-0 Euro 2016 qualifying win against Group C minnows Luxembourg in October.
The 26-year-old Chelsea forward has returned to the squad after a series of niggling injuries and will have another chance to show his worth if coach Vicente del Bosque deploys him in Spain’s qualifiers at home to pool leaders Slovakia on Saturday and away to Macedonia three days later.
“I never regretted choosing to play for Spain and I want to repay the confidence that has been shown in me,” Costa told a news conference at Spain’s training base outside Madrid on Wednesday.
“I am feeling better physically all the time,” he added. “I know I can give much more and hopefully that will start now.”
With six matches played, Slovakia top Group C on a maximum 18 points after their surprise 2-1 over Spain in Zilina in October.
Chasing a third consecutive continental triumph, Spain have 15 points at second, with Ukraine a further three points behind at third.
Costa agreed with a reporter who suggested anxiety may be hindering his progress with the national team but said he was feeling more at home in the side all the time.
“It’s very important to me personally to perform well and score goals as that will give me confidence,” he said.
“There are no excuses, I need to do better. I haven’t done anything yet and I think I can give a lot more.
“I am in a team with the current champions but I am feeling more comfortable all the time and closer to my team mates and that’s very important too.”
(Reporting by Iain Rogers, editing by Sudipto Ganguly)