Wendy, I bet it's not lost on you that you've got some of that perfectionistic, black and white thinking thing going on about your grief group. Maybe we can get it to mellow out a bit, which would make it easier to get your mind and psyche around, and then less difficult to change.
No one can say if it will ever be "totally better" regarding you opening up in the group. You know what I'd say, right? That thinking about it that way will only box you in, make you feel threatened, and ultimately keep you stuck. You'll have much better luck, and avoid a considerable amount of frustration, if you conceptualize it one group (or even part of one group) at a time.
First of all, it's crucial to remind yourself that everyone expresses grief (and all emotions, in fact) in their own unique ways. Some people find it natural and/or helpful to speak a lot out loud about their experience, others gravitate toward writing or art, while others sing, walk, swim... you name it. Being in a group is a terrific avenue for talking, but there are other reasons to be in a group- listening, being not-alone, relating to others' experiences... maybe you could start, if you haven't already, by letting yourself be clear about what draws you to the group at all. Maybe you do want to talk, maybe not, maybe sometimes... who knows. Definitely try not to have a pre-conceived notion of what you "should" be doing in the group.
If there are times you want to talk, you might try saying something just ridiculously small and brief. And I mean ridiculously small, so small you think it's even silly to bring it up. Now, the perfectionistic part of you might say to me, "but that's dumb, why even bother, and anyway, I have a lot more than just one little thing to say." And I'd say, "yes, I get that. But if you don't start small, small enough that you are pretty convinced that you couldn't possibly have taken up much time (you can even look at your watch before and after you speak, to "prove" to yourself that it wasn't much time- I'm sure whatever you'll say will be shorter than what other group members are saying) you'll never trust yourself to talk more freely."
I once worked with a client who was terrified of grapes. She was terrified of almost any food, but there was something about grapes- I think it was because she really liked them and very much wanted to eat them. She was completely unable to eat even one grape. She could say, rationally, that she understood one grape didn't have many calories. But what stopped her was her fear that if she had even one, one little grape, that she'd "go all the way over to the other side, the dark side" and eat grapes out of control, and never stop.
I was reminded of this when you mentioned being afraid if you began to talk, you might never stop and then go totally overboard and in effect "consume" the group.
I have millions of stories about things people are afraid to try a bit of because of their fear that once they start all hell will break loose and they'll be out of control forever. Just this past week I heard people talk about this in terms of: crying, being mad, eating, drinking, resting...
I know it is hard to trust that if we let ourselves have a little it will be ok. That starting does not necessarily mean hurtling toward chaos.
I'm hoping, Wendy, that you can cut yourself some slack here. It seems to me that you're being too hard on yourself about not doing the group correctly. If so, this is a bummer for at least 2 reasons: you don't get to talk if you do want to in the group, and, you end up mad and/or critical of yourself (in addition to sad that you didn't get to talk) because you didn't speak up.