Eating from the back of the mushroom made you shrink.  You take a second bite from the front in hopes of returning to your normal size.  Before your second bite can take effect, the queen arrives with her deck of cards.  Someone has stolen her tarts, and she is out for revenge.  Upon seeing your size-morphing powers, she believes that you would be tricky enough to have stolen her tarts.  She orders the deck of cards to arrest you.  

Of course, you will be granted a trial among your Wonderland peers.