whats wrong with my 1996 N vauxhall vectra?

hi please help here are the symptoms

whenever the i start the engine the tempereature gauge goes above 100 but not on the red lines and only drops down to 90 when driving.
what i have recently had repaired
new head gasket
new skimmed cylinder head
recent as in 2 days oil change and oil filter
the water pump and radiator thermostat are both fine before i did an oil change i had plumes of white smoke when i revved engine now the white smoke is still there but minimal i beleive this is water vapour please help me i need to know whats causing temperature to be so high its a 1.6 ltr 16v