A better idea would be to add a pipe or door somewhere so you can reload the level. Even if there were 2 or 3 p-switches, if the player doesn't know where to go they could use them all up and be stuck.
Think back to the ghost houses in SMW, which often had p-switch puzzles. They always had a door that let you leave and come back to try again.
You probably have too many ExAnimation entries. Taken from the LM help files:
Note: Although there are 0x20 entries allowed, the game usually can't handle that many extra animations. The top of the screen will start to flicker when you've exceeded the limit. In testing a typical level, I was able to get up to about entry 0x12 for animated 16x16 tiles before flickering started to occur. With just palette animations, I was able to use up all except the last entry before any flicker occurred. YMMV.
Pretty much what ibz said. The level lacks any real design or detail. Good levels usually have a lot of interesting scenery and variations in landscape. You don't have any bushes, extra coin blocks, pipe decorations, bonus areas (aside from the clouds in the sky), or anything else worth mentioning.
When in the event editor mode, use page up/page down to scroll through the events. If in Layer 2 Event Editor Mode you can also use home/end to move through each tile placement one at a time. The bottom of the screen tells you which event and which step you're on.
To trigger events, click a tile while in Layer 1 16x16 Editor Mode, and go to Overworld > Modify Level Tile Settings -> Event to activate when above level is passed.