Welcome on NUMA ! :)
For a first map, it's good.
Hyques is right, the 9 mines at the middle are uneeded.
remember one thing : each time you add an object, you make the loading time longer (I'm not talking about the tiles).
So, when you can, try to delete unneeded objects, unless there's really few objects and it serves the design of the map.
Try also to see where your map could be cheated : for example, your one-way, on the upperleft, is too close from the switch : it's easy to catch the switch before going too far and turn back to the left.
There are many ways to cheat in N, you'll learn them soon.
Something else :
Don't make traps. As they are funny for the maker, they are anoying for the player...
I was killed by a trap door at the end (from behind), and that way, I'm not sure the map is possible (or is it a puzzle? I doubt about that)...
Can you put a completion demo online ?
Keep up the good work !
:)

The mines. You could have used just one.