Yes you can, no need to complete the order. As far as I understand it, this is the rare occasion where you should send an email to shop@jolla.com.
Once you have sent an email with your order number and a request to cancel, please be patient. Check back in the forum before sending more emails to Jolla. You will get your refund eventually, but it is likely to take several weeks.
Jolla has a lot on the plate atm, due to sub-optimal instructions in early emails and people not reading the whole email before acting (me included 
).
Also people getting anxious and sending reminder/follow-up emails. Don’t do that - it will only serve to delay processing for everyone.