Planaria are very common when you over-feed your fish, I guess they get in on plants and with new additions. You're right, they're nothing to worry about but I would NOT boil the gravel, you could end up creating a mini cycle because a lot of beneficial bacteria lives in the gravel. Simply minimise feeding, stir up the gravel once in a while (your fish will appreciate the snack if you're feeding less) and vac the gravel more often.
Oh and Goldiegupp, your signature is bizarre! That's like, the nightmare tank!