Desperate: Can I cover roots on permanent dye job with at-home semi-permanent?

[SuperConfused]

Am going away for 3-week long work trip on Saturday. Had planned hair appointment to deal with quite noticeable roots tomorrow but that has been cancelled and have no time to fit one in before I go.

I've never done at-home hair dye but have been considering it, currently the hairdresser does all-over permanent. I'm wondering if I buy a semi-permanent and do it myself tomorrow night, will it manage to make it all the one colour and make me look less unprofessional? There will be no chances to dye my hair where I'm going.

Currently my natural hair would be (I think) sort of mousy brown-to-auburn, its dyed a (lovely!) auburn/copper colour that most people don't realise is dyed. I've found it quite hard to avoid that red-hair-that-looks-artificial colour but my current hairdresser has cracked it. I'm worried that if I get something over the counter it will either a) make it go purple/green or b) make it look that kind of plum-y fake colour, which looks great on some people, but is not for me.

I also don't know if I should go for permanent or if semi-permanent is a no-no on top of permanent hair colour. Despite dying my hair for over a decade I've never done it myself.

Work near a big boots so my options are pretty much limited to there.

Anyone have any guidance?

Go for something lighter than you think you'll need. Castings semis are pretty good. There's a few with Honey in the name which would look goldeny and warm. Look ones with a number starting with 6 or lower. Higher than 6 will be too dark

I do a semi-permanent inbetween my permanent hairdresser visit. So I do hairdresser, 5 weeks later, semi then 5 weeks later hairdresser. My hairdresser says it's fine to do this. Saves me quite a lot of money and my semi-permanent colour gets so many complements for being a lovely colour (unlike my hairdresser one). It's dead easy to put on, I cover the whole head but concentrate on the roots and hairline. I use Boots Botanics Warmed Terracotta Autumn or Auburn. Good luck

Thank you, this is very reassuring. Will hit up boots in lunch time tomorrow and keep fingers crossed that I don't go too far wrong.