You are rushing and you lack self-confidence about this part of the layout. You are taking shortcuts that only serve to help to continue the cycle of self-doubt.
Why did you not mask off the tunnel portal? Why didn't you experiment with some lighter shades and and test them under the lighting first?
For what it's worth, I have two observations: First, the lighter colour is much more realistic in the first photo. You could try a light blend of light grey and some lighter tan and see if that works better for you. The lighting also has an impact. Secondly, your painting doesn't seem bad to me, only your approach to it...at least, I say so because of your expression and what I see in the images.
You need to take a deep breath, step back, admit that you must re-think your approach, and understand that nothing you have done so far is cast in concrete. You can change all sorts of things with more paint, cutting out something and addind a new shape inserted in the gap, and you could even fiddle with your rails at this point if you decided that it was the best thing to do.
Slow down, don't take shortcuts, take the time to properly prepare a site for painting, and do experiment with mixes of paints and lighter shades by painting small areas, sprinkling a bit of ground foam, stacking a locomotive and a 'tree' there, and taking a photo. Does it look okay under the lighting? Then you have your paint mix and can continue.