First and foremost, as others have posted this is too late to worry about it, AND there is nothing to really worry about.
BUT, if you want to approach this as a fun sort of science-fair project that will only tell you 'IF' and not 'HOW MUCH', read on.
You have 3 dirt-cheap and easy ways to detect radioactivity:
1) take an unexposed roll of film (B&W might make it easier to see) and place it near to suspected source. Go develop the film. If you see alot of 'static' then there might be something there. (make sure the place that develops it does the whole roll and doesn't try to malipulate/enhance the image for you) Tell them you will pay for all frames including the 'blank' ones. *For bonus points, you make a frame that you can mount strips of unexposed film to and 'aim' the film at the suspect areas. (make sure you keep the film away from the light)
2) (must be done at night) grab an old phosphor screen (like from an old television), as radiation hits it you will see small flashes of light like static
3) Use a smoke detector. as beta particles pass through the detector, the alarm will go off