If I started a fight against an opponent my pet can't beat by accident...is there any way of getting out without it losing all its health?

- Find your pet on the statistics page and there should be a link to withdraw from your battle.

I see a link saying forfeit battle...would that mean it gets counted as a loss but no health is lost?

Yes, it would count as a loss unfortunately, but your pet will keep whatever health you have right now :)