Some cards in my deck are heads down, can opponent force me to fix that?
Nobody but judges are allowed to look at your deck during the game. You will need a judge to fix your deck.
During a game, you would obviously not be allowed to look through your deck unless an effect would allow you to.

401.2. Each library must be kept in a single face-down pile. Players can’t look at or change the order of cards in a library.

In a tournament setting, your deck would count as marked, and you would get at least a Warning for it, possibly a game loss:

Tournament Error — Marked Cards
A player’s cards are marked or oriented in a way that could potentially give an advantage to that player.
Penalty - Warning
The Head Judge has the option to upgrade this penalty to a Game Loss if he or she believes that a player noticing the pattern of markings would clearly compromise the integrity of the game.

Only a judge would be allowed to fix your deck as a remedy to the infraction.
If the error was not reported, and the Head Judge is convinced that you knew it was illegal, and that you intended to gain an advantage from the cards' orientation, the infraction would probably be upgraded to Cheating, and you would have to get a disqualification.