Lupis,
There are a few tricks in braiding that will look like you have made a loop at both ends, but non that are easy to explain and still strong.
The best I can do for you now, twist 2 of your strings and bend them into a loop, and splice the other 2 ends in from the other side, see:
http://knopen.ismijnhobby.nl/tables/twist_to_braid_table.html That is if you braid with 4 strands.
It will be stronger if you go on with splicing in into the braid below the loop.
You can do the same when you work with more or fewer strands, but of those I do not know an explanation on the web.
You can also splice the ends into the braid, you get the same results as Justknot has in his braided sling tutorial,
http://slinging.org/forum/YaBB.pl?num=1170457410, third photo, but that is not easy to explain.
Willeke