Right, red is hard to get rid of. You will be a bit rusty and warm for a while.
I sometimes recommend people strip out their colour with ColourB4 and start again but now you have started having highlights I would carry on with that personally. If you go back, see if your hairdresser will "tone" the highlights for you using a toner. Also, if your highlights are quite light but just a bit strawberry then you should get a Lee Stafford "Hot Shots for blondes" - which will add an ashy tone to your hair and help neutralise your brassiness.