Hi Sophie,
Firstly I’m sorry to hear of your bad experience. Unfortunately it’s a common misconception that Ombré colour is an easy look to achieve, however it is actually quite an advanced and lengthy technique, so I’d always recommend you visit a salon that specialises in colour in this situation. The best way to check if the salon offers quality hair colouring services is to check to see if they are certified with any of the main colour houses such as Redken, L’Oréal, etc, as this tends to be a good indication that they have been trained in such techniques to a high standard and should have proficient knowledge.
The good news is there’s no reason why your colour can’t be altered to reflect what you originally hoped for. I suggest you visit an expert colourist. They should not add more bleach to your hair, it should be fine to apply colour in order to lessen the stark contrast between tones. They will more than likely need to pre-treat the hair to ensure the condition is right for colouring, as you’ve recently had a service and I’d recommend a post-treatment to restore elasticity and help your hair look healthier.
Before you book back into a colour specialist, request a consultation to give you the opportunity to see some of the styles being produced in the salon first hand. Whilst it’s always great to take pictures of your desired style along perhaps see what images the stylist produces so you can see if you are on the same wavelength and that they are fully aware of the look you hope to achieve. Only book an appointment if you feel comfortable.
I also think it’s worth you contacting the salon where you had your hair done previously, explaining that you were disappointed with the experience and final result in order to request a refund.
During the interim period, try wearing your hair in a bun to disguise the sharp line between the two colours. A bun will hide a multitude of sins and are also still on trend for the season.