I'm also in the UK and do agree it's masculine sounding to a certain extent.... but it's not like calling a girl Trevor is it!!!? Although she may get a girly middle name, you have to remember it won't often be used, so having real confidence in the first name is going to be essential.
Even the spelling might help... could it be Elliotte or something?! lol I don't know. It would just help people realise she's a girl (if you have one) when they see it on paper. It may sound daft but I'm a teacher and that stuff helps when you just get a list of names when they start school and so on. I'd 100% assume 'boy' with the name Elliot. Although, some other names now cross over genders easily, Morgan, Rowan etc. So Elliot may also!