your best bet is to pick up a sterile 10ml vial (better yet, get a bunch, like 25... for the future), and a few .45 and .22 whatman syringe filters and a few 10ml syringe and a few 18ga needles.
draw out the deca you have, into the 10ml vial.. remove the 18ga needle... attach the syringe filter and a new 18ga needle, filter the deca into the new 10ml syringe barrel, then attach the .22 filter and new 18ga needle and filter into the new sterile 10ml vial... then try an injection.
if it still hurts, it's from a high BA content. whoever made it probably used 5% BA and little to no BB, instead of doing the standard 2% BA and 20% BB.
I do everything 2/20, even deca, enan, and eq.. even though they'll hold with very little BB (if at all)