Hair Flipping Up and Out

A: This sounds like a combination of styling issues, neck/shoulder contact, and cutting technique.
The Haircut
To encourage the hair to curl under, the inner layers - the layers of hair closest to the scalp at the neckline - are slightly undercut (cut shorter than the layers above them). This cutting technique removes excess bulk underneath and encourages the longer outer layers to cup inward over the shorter hair rather than resting on top of it and kicking outward.Be aware that undercutting the hair at the back of your own head can be notoriously difficult to execute without a multi-mirror setup, as it requires precise, even layering at the nape.
The Styling
Apart from the haircut itself, styling can make a significant difference:• Flat Ironing: You can use a heat protection spray, in conjunction with a flat iron to smooth the curves into a flatter configuration. Work with small sections and use only enough heat to reshape the hair. Let the pressed sections cool completely before combing through them, or you will undo the hydrogen bonds while they are still pliable and lose the shape.
• Blow Dryer & Round Brush: Use a round brush in combination with your blow dryer to style the hair to curve under gently in the back. Aim the airflow downward along the hair shaft while rotating the brush slightly under as you dry the ends. This smooths the cuticle, adds shine, and directs the hair inward. Finish each section with the cool-shot button on your dryer to lock the shape into place.

Keep in mind that you might just be in an awkward stage. Hair often flips out at one specific shoulder-resting length, but as it grows a little longer and gains weight, gravity naturally pulls the ends down so they lie flatter. If you are in that in-between phase, a little patience combined with the right heat styling may be all you need until it grows past your collar or shoulders.
©Hairfinder.com
See also:
Flat iron styling
How to blowdry hair
Undercutting or inverse layering