Here are four variations on the bowline, in words and graphics.
Note that all four of them are here left not fully dressed (not tightened).
In each case, the standing part should be pulled, or at least held firm, to tighten the knot.
If, instead, you pull on the working end without holding the standing part -- and this seems to be your problem -- the knot ...
The bowline is an interesting example of a knot which fails if dressed wrongly - even if it has been tied correctly.
If you tighten a bowline by pulling on the working end, or by pulling the loop apart, it can invert to a running noose.
Tighten it by pulling the standing end to avoid this.
Here is a loose bowline:
Pulling the working end (and the right-hand ...