It is appropriate to take your turn at the front. It doesn't have to be for long but at least you showed your appreciation by taking your turn. However, if you are hanging on for dear life just let them know and they will probably be glad to help you along and that will improve your skills to return the offer to someone else.
I don't think anyone would have a problem as long as you communicated with them.
The fact that there were other cyclist in the group made it less of an issue that you should pull.

I do agree...thank them for the pull and all will be well.

Crash