Hi Mick, welcome to AF.
Probably too late to help this build, but I try and get rid of all the imperfections whilst still at the grey primer stage. Only when that is acceptable do I start with the white. In fact I find it easier to spot imperfections with the grey.
Also, if you have an airbrush, there is no reason why you can't respray just the affected area, so as not to build up too much paint all over the whole model.