I have a small groin hernia that I'm getting fixed in about 2 months, dull ache but doesn't hurt. What is my chance of a strangled hernia in 2 months?

Small. While any hernia can incarcerate (get stuck) or strangulate (loose it's blood supply) at any time, the chance of it happening in a two week period is pretty small. If you have a very painful lump that does not push back in, go to your nearest emergency room. .
Low, but not. zero. Avoid straining, heavy lifting, coughing, or anything that might apply pressure to the area. If hernia becomes incarcerated, it requires emergency surgery.