Partial app download using up space

I posted this to the ios 7 forum (phone is iphone 5 with ios 7.1) but I now think this is the right forum. Sorry for duplicate post but I am a bit desperate

I am on holiday and wanted to download tomtom Europe. I had 2.3gb of space which is enough to install it



About half of it downloaded then the phone came up with an error to say the app had failed to download



I tried again and found I no longer have enough storage! Only 1.3gb left. I tried deleting the app and re-installing but can't get my space back...



Things I have tried: erasing content and settings, rebooting, signing out of App Store.



I haven't done a full reset since I am on holiday and don't really want to restore my whole phone over dodgy hotel wifi...