Your whole pond thing is wrong. Use the tiles correctly, it's one big tile error.
Change the path, do the outline and then fill it with just the middle parts and you shouldt have any problems with it. and remove those things at the front of the house, actually remove the whole house and re do it.
I suggest looking at other peoples levels and learning from them, but atleast you're trying and it's a good start
Check other peoples levels out on the forums. and learn, I found that to be the best way.