Tamehana said the weekend's games were two which got away from his young side who had shown promise in thrashing Poverty Bay 48-10 in the series opener the week before.
"If we executed a few plays we could've been in the fight," he said.
"Our set piece wasn't too bad, it was just wrong options and the wrong time."
Tamehana said Horowhenua-Kapiti had a couple of opportunistic tries in Saturday's game but Wanganui were still in touch at halftime.
"It was in the 2nd half they got away."
While Wanganui pounced on Poverty Bay's lack of structure the week before, Tamehana said his side struggled against more disciplined teams.
"[Poverty Bay] were quite loose which complemented some of they boys which were used to that type of play," he said.
"But Wairarapa and Horowhenua-Kapiti, they were a little bit more structured and a little bit more classy.
"Horowhenua-Kapiti are very strong across the board and they probably had the most classy backs throughout the tournament.
"But the other side of the coin is their were still four (Wanganui) players picked for that Heartland team so it's still a good thing."
It was a similar story in Sunday's game against Wairarapa Bush with Wanganui in touch at halftime before the Masterton-based side surged to win the match and claim runner-up for the tournament.
Two games in two days was tough, Tamehana said, but a good test for the players.
"Everyone's in the same boat. It's just the nature of the tournament. That's something the selectors probably look at, how players deal with it."
Tamehana said while about four won't be back next year the bulk of the squad would be together for a year or two.
"It's quite a young team. We did well considering. I'd definitely like to be part of it again next year."
In hindsight, he said the preparation had not been strong enough with only two training sessions in a short window.
Tamehana picked Jason Myers as the standout player for Wanganui throughout the tournament.
"He definitely went to play rugby, that's for sure. He really asserted himself."
