I spend a lot of time pressing seams open.
And, you might try steam while pressing ...
one of the threads in this forum was talking about POUNDING the lumps into submission ...
lo and behold! The quilting industry has come up with a rubber mallet for the deed.
You might try the local hardware store for a construction rubber mallet, since it will probably be cheaper. Won't be as purty <g> but hey! What you really want is the mallet, right??? LOL