engine managment light flashing plus audible alarm sounds drives great

I had the wrong dipstick in the engine so I kept getting 3 audible pips everytime I braked or turned acorner so I bought a new dipstick from Peugeot and filled my oil level since I have done this my engine mangment light keeps flashing catalytic converter fault and antipollution fault with asingle beeping only just had my 1.4 307 mot but they also said someone had fitted the wrong exhaust system the car drives very well if I keep driving will I damage the engine I only use it localy and never take it over 35mph