If you aren't able to get it to mount, just plug in your ubuntu bootstick and mount the partititon. Use either gnome-disk-utility or just access /boot on the current ubuntu live session via `sudo nautilus`. It should work. As this is a fresh install you should try reinstalling it again from scratch.
It's likely that you can't access windows now as its stuck on the grub screen. Access your BIOS and switch the UEFI boot order such that windows boot manager is first. But even that is likely to have ubuntu as the only entry. Not always, but there is a small chance.
If you can't access your ubuntu bootstick because of the above reason, try disabling UEFI boot from the BIOS, and then boot using the boot device selection menu.
Later on, you might want to try out the Refind boot manager, you can install it through ubuntu and you will always be able to probe any new UEFI/non UEFI devices you insert for operating systems in case the BIOS order is overwritten again.
And you aren't likely to get much tech support here because this place is filled with mostly illiterate useless enginiggers whose only aim in life is to be a wealthy wagecuck. Go to an IRC channel like freenode's #ubuntu.