SEO for an ecommerce clothing website hosted by shopify

Hello

I have just launched a new ecommerce website hosted by shopify.
This is selling ladies fashion at affordable prices.
I need some basic SEO doing, I have two critical errors 404 or something like that and when I type in my business name on google I am nowhere to be found.
I must make it clear that I do not expect to be up there with boohoo or asos anytime soon, I just need the errors fixing and the website to appear when you google it without typing in the full web address.

My budget for this is currently £100 per month. Please do not quote if you are going to charge more than this as it will be instantly declined.

I appreciate that with this budget it is going to take some time to complete what needs to be done however this is the maximum I can afford right now.

I am doing instagram advertising and facebook and will increase this budget the moment I start getting a few sales.

I am looking for someone to start work instantly on this for me.

Once the basics have been done I am happy to pay more for things like link building and any other recommendations you may have.