I'm pretty sure deadeye means you not using a different object for the stump - this saves video memory and lets you place the stump as you wish.
Now! LegendaryBlade, listen up!
Pay close attention!
What you are doing is wrong!
Game graphics are not made out of one large image. They're made up of tiles. This is because games are terrible, terrible memory hogs. Small tiles allow you to put the pieces together like a puzzle to make a bigger picture. You can reuse a small tile as many times as you like and there will be very little impact on memory, because your graphics card only has to remember how to draw the small tile just once. It can make a million copies in the blink of an eye with no problem. But large images on the other hand take up precious memory and if you use them then you are going to jail.
Okay then, here is your new grass tile:
Wowowee! It's only 64x64 pixels! Amazing. And you can tile it forever and it repeats seamlessly and everything.
I've also updated your .cap file with all the other graphics you had in yours... take a look at it now.
As you can see, the tree stumps and rocks have been made into separate objects that you can put wherever you like. There is also a separate collision layer with a hidden solid tile for Sonic to run on. Now the doors of perception have been cleansed.
On an unrelated note, you won't be able to make a Sonic game using the Platform behavior. I guarantee it. You will need to make your own platform engine using Custom Movement behavior, or by coding the whole thing from scratch with events. Also, you're very likely going to need a separate hitbox for your sprite. Per-pixel collision is bad news when it comes to platform games.