It's normal to have a high sugar after a race like that. I'm not sure why they even check it.
Your Na. (Sodium) was low, but WHY is the question. Having a normal BUN/Crea and still having huge weight gains is not normal.
You could have to physiologal things going on, more than 2, but I'll state the 2 obvious.
1) You have weight gain because your blood sodium is to HIGH and therefore your body hold water to dilute your sodium. The problem with that is the fluid isn't usualy held in the plasma, but the third space. (The area between your vessels and muscles.)
2) You have hyponatremia caused by fluid overload. To much water intake and not enough NA intake. Again the problem here is where the water is. Additionally, if you had taken more salt, you MIGHT have been in situation 1 even more.
The BUN being normal means you had enough water. The Crea being normal means you were clearing the water. Since the BUN wasn't LOW to much water and your crea wasn't low, in this case, I would guess you were just low on sodium. Moderate low, not freak out critical low.
You said you were urinating on course and after the race so it would appear that your kidneys were doigng what they should have been.
This looks like a simple case of moderate hyponatremia caused by fluid overload.
We are gonna get this right... Start adding all the drinks you can remember so we can add it all up.