I got eighth place, and it'which is the last position towhere you receive a medal and certificate!!! I got eighth place, which is the last position where you receive a medal and certificate!!!

How lucky I am I!!!! How lucky am I!!!!

Your version is not incorrect but sounds very old-fashioned to me, haha. This is the version everyone says now.

To be honest, I had to walk at several timespoints during the race because I couldn't stand the astitche in my bellyside, but the result is still good!! To be honest, I had to walk at several points during the race because I couldn't stand the stitch in my side, but the result is still good!!

This is totally understandable, and I don't see any errors. Now that I see @cptyossarian's feedback, I realize you are writing about a race. I updated my feedback with that idea in mind. I wrote this earlier, when I didn't understand the context was a race: A native speaker would probably not say, "I had to walk several times" because it doesn't give a clear picture of the situation. "I had to walk out of the room several times," or "I had to leave and walk outside several times," etc., would provide just enough detail for us to picture what you mean. By itself, "I had to walk" would be used if the bus didn't come, your car broke down, or your bike got a flat tire. I don't think "still" works here because the pain you felt is unrelated to the result. "Still" means "anyway" but the two things (pain and result) are totally separate. Being nervous has nothing to do with your score. Does that make sense? If it was about a race, then slowing down because of the pain is related to the result, so "still" makes sense! One easy way to avoid this kind of confusion and useless feedback in the future is to use your title to tell readers any essential information that isn't included in the post: for example, "The Race."

To be honest, I had to switch to walking several times because I couldn't stand the ache in my belly, but the result is still goodgot horrible stitches, but I still placed well!! To be honest, I had to switch to walking several times because I got horrible stitches, but I still placed well!!

Your version is grammatically correct. My changes are just for more common wording. A "stitch" is the pain in your torso from running/exercising.