There are two options:
1) If you know you're not near any Controlled airspace, take your last known position on the chart, draw a circle around it the radius of which is the distance you know you will have flown since that point (so - if it's 5 minutes at 120Kts then that's a 10nm radius). then work out where you are inside that circle by reference to ground features
2) If you suspect you're near CAS, or (1) above doesn't work, dial up 121.5, squawk 7700 and shout for help (PAN call). There is no shame in doing so, you'll get all the help you'll need, and it'll stop you having a nasty with something bigger and faster.