I have been mewing for about a year now and while I had some minor issues before, this is new to me. You can see the problem in the picture, it seems as if my cheeks and my tongue are getting in between my molars. It happens automatically and I'm not sure what to do about it.
Background:
Throughout this one year of mewing I have tried different techniques and although I have seen a lot of progress, it is still not clear to me how to do it correctly. When I first started I barely had space to flatten my tongue, so I did what I could. When things got better I tried balancing the force of the tongue with my teeth together and was pressing mostly forward with my tongue. After that, and this worked really well for me, was to have my far back molars together (slightly clenching, especially when swallowing) and sucking continuously on both the palate and my teeth while pushing forward and up. However, for some reasons this does not really work for me anymore. Now I am trying to have my teeth slightly apart and pressing forward and up as hard as I can.
It seems as if there is no clear consensus on what the correct way is. I have also noticed that mewing wrong can reverse some of your progress really fast and that stress also plays a big role.
I’d recommend to have the teeth together, because when they seperate you’re at risk of lengthening the whole face.
When you begin to mew suction hold, do a mew cheesy grin and any suction between your cheeks and teeth should break.
Remember this pain... and let it activate you.
Don’t clench your teeth. Dr. Mew has a video on HOW TO NOT DO THAT. I would go the simpler/easier route... of getting mechanical expansion. Too much stress.
Edit: I cannot give personal advice - not a doctor - but I took a look at your photo and your teeth look quite nice from what I can see in the photo. What are you trying to fix?
Mewing has less to do with ones teeth but more with the face as a whole (and even with body posture). Before I started mewing my palate was much narrower, my face was more asymmetrical, I had pretty much no cheekbones, and I had an uncomfortable feeling in my jaw. One of my eyes was also smaller (probably due to the asymmetry). All this has improved a lot and this has convinced me of the benefits of mewing. It's still hard work though and its difficult to do it correctly.
Also, do you have a link to that video?