Using a guitar strap will help. The soundbox part of the guitar should be held vertically, the back of it resting against your body. The upper half of your right arm rest on top of the lower bout while the right forearm is free to move in front of the guitar's body. It's basically your right arm which is holding the guitar in place against your body, and wearing a strap can help with this, providing the strap is tightened enough to bring the guitar in against your upper body.

Playing standing with a strap can really help to get the guitar in proper position.

When you look down at the guitar, you shouldn't be seeing the top of it, you should be seeing the side of it. Likewise, you shouldn't be seeing the fingerboard, but the side of the neck where the position dots are. If you need to tilt it slightly now and then to check the left hand position on the frets and chords, fine.

The end of the neck where the nut and tuning heads are should be at about eye level. This means the guitar is tilted up at that end to about a 45 degree angle.

If you're sitting, then you will need to rest the guitar either on a raised right knee by using a foot rest under the right foot or by crossing the right leg over the left leg. The true classical position, on the other hand, has the legs apart and the left leg on a raised foot rest and the guitar rests on both legs, but is raised at the left side.

Look up some videos on Youtube that show classical guitar technique. There are several.