Hi
If its only acrylic you have a couple of options:
- you dont have to put anything on it, but it may get dusty over time...
- clear varnish . I would recommend a spray one, you can get it from Spotlight I think or any art shop. You prob just need a very thin coat of it - but make sure that you spray it outside and prob best to wear a mask or scarf around your face. Look for a 'matt' finish one rather than a shiny one.
Check out this site for some tips / info:
http://painting.about.com/cs/paintingknowhow/ht/Howto_Varnish.htm
Well done for being creative - what did you paint?