Scared of pooing on the potty

[hazbaz]

I know this is not unusual but I'm really hoping for some advice before we end up with an issue.

DS2 is 2.10 and we started potty training 3 days ago. So far he has done 1 poo on the loo and 1 in his pants. Today he is clearly withholding his poo....

Prob is one night I took off his nappy before bath and asked him to sit on the potty (been doing this before bath for a while no prob) then dashed downstairs quickly and he'd done a poo and was standing there saying Mummy there's mud in wee, disgusting!

He is now scared it seems and if he needs a poo always says no mud in my wee Mummy.

Do you reckon I should just shove him back in nappies for a while so he forgets or just plough on with lots of reassurance (& bribery)