You are using the stock Intel fan, correct? The push pins that Intel uses for the fan can be a little tricky to get on. You probably haven't got them down properly. Otherwise your temperatures shouldn't exceed 50C or so, even under a full load on both CPU cores.
See this little image:
To remove the fan:-
1) Disconnect the CPU fan cable from the connector on the motherboard
2) Rotate each fastener on the fan counterclockswise
3) Pull up two fasteners at a time in a diagonal (start with the ones I circled in green in the above image) sequence. This will loosen the fan from the motherboard.
4) Carefully pull the fan up and off the processor.
Now try putting it back on, making sure all four of the push pins go down properly so the CPU fan is securely attached to the processor.
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