I have two thoughts about that:
* If you like to play in two or three tournaments at the same time, you may want to try joining some of the official chess.com tournaments (those which are not organized by the members but by chess.com staff). I think I remember that these tournaments do not fall under the "one tournament only" limitation for free members.
* If you have come to like playing in some of the member-organized tournaments, it might be an option for you of course to try a premium membership. I think you can start on a monthly basis if you want to, and from what I have gotten to know here on this site, it can very well be worth the moderate financial support connected with it
I'm a free member here at chess.com so I can only do one tournament at a time. The current one I'm playing (my first) is the King's Indian Game one. I will be eliminated this round (came in 3rd of 6.....) and there is only one more game occurring in my group (the outcome of which won't affect anything). If this game is still going on come June 1, is it kosher to withdraw from the tournament in order to join another one?