Giveaway Cap

Wait for your giveaways to get marked as received, make more giveaways, rinse and repeat. Pretty sure the amount of giveaways you can make at once will expand as you make more completed giveaways.

That's how it was with the old system. Every time you successfully gave away a few games, you got another slot. I can't remember if the new FAQ mentions slots, however.

Old system gave you a new giveaway slot every 3 successfully received. I don't believe this has been changed. It was implemented to prevent people from spamming fake and exploited giveaways.