bike running hot

My tt600 has an issue.
It runs hot.
ive just stripped the engine and did work on the head and it was all within spec.
Put it all back together with new head gasket and its the same.
Gets hot quicker than i think it should and on hot days will not drop below 100 unless your cruising at 50+.
ive checked thermostat and thats fine but it gets hot just idling.
Could there be a faulty sensor causing this?

 

Thanks for your reply.
I went for a ride yesterday and i noticed the temp guage jump up and down and then read a fairly constant 103-105 so i think the sensor may be faulty.
I have ordered a new one so i will see how that goes first then post it up in here.