heater problems

I bought an aqueon 10 watt heater for my unfiltered 3 gallon..someone told me it would not heat up enough for that size if tank..ok..so it took for ever to heat..i even thought it was not working..so i wake up this morning to find that the temperature is 95..its not adjustable..should i take it...

so far i have figured out that the Petco brand thermometer that i have is a couple degrees off and Preset heaters make me frustrated. i'm still trying to figure this water heater out, Hydor 7.5w heater (the one that looks like a heating pad). it works fine when the bottom is touching the wall...