A flaw in my betting pattern?

[Mosselmaniac]

I'm playing HU sit and go's lately, but i encounter this problem too when playing any other s&go on low stakes.

For example, when i hit the nuts, or when i feel like i hit the nuts, and i do have some action till the river, i decide to make a value bet, like 2/3rd of the pot. i get paid off this way often enough, however, this leaves me behind with the question: "What if i had bet more?". I have the feeling i give my opponent (especially in HU) a chance to come back in the game.

For example, i have trips and the other guy shows 2 pair on the river. I'm almost sure that he'd have called my bet on the river with that hand, even if it was 2x the pot or something. The amount to bet, is likely read-dependant, but often i just bet 2/3rd of the pot...

Any advice?