Yes some pepople have reported bitemarks. If you are that young, I suggest you implement body posture first, then oral posture (there's a lot of info on this forum about oral posture, but since you are 13, you should just try to put the tongue on the roof and slowly improving and getting more of it up there). Also start chewing and swallowing more adequately. If you don't go crazy there won't be any dangers since mewing is how the body should work naturally. Of course it' s worth it.

Is it bad to start with the whole tongue. I have been doing this for a few weeks and putting my whole tongue up there has become easier. My mouth top teeth have been feeling weird too. Is this a sign of the palate becoming wider? Is it possible for mewing to make the face look worse??? Us it normal for the tongue  to hurt? I got a lot of questions and I appreciate those who take the time to respond to them!!! 

What do you mean by going crazy? I do focus on mewing a lot but I don't hard mew.

If it's no problem for you to get your tongue fully up then sure do it that way. New sensations at the beginning are normal don't worry. What I meant by going crazy is don't apply some radical theories that are out there just to fasten the results. You are young enough to correct yourself with just posture. Also I forgot to suggest you tongue chew to train your tongue. You can train your tongue by hardmewing too. Take some pictures of your profile and measure your IMW every now and then to make sure you are progressing. 

Ask your parents if they can have you see a myofunctional therapist, or even Dr Mew

Dr. Sara Hornsby can even do online consultation. 

Does mewing cause TMJ? Also, since the teeth on top are moving will the bottom ones move too?