The 0.00007057 is the bitcoin in interest that's due - there's no % - (ie it's been added to the amount you've borrowed)
Interest is calculated every hour based on that (I think you get an email summary at some point too that might provide more useful information than the live info).
The amount of interest in BTC shown in my wallet has now gone up from 0.00007057 to 0.00009097...
See here...
https://postimg.cc/v1DdCgsj0.00009097 BTC is roughly $3 (just under)... is this the total interest I owe or do I have to multiply this by the number of hours I've been in the trade? I've been in the trade for around 5 days now so if it's an hourly rate it's gonna cost me a bloody fortune!