what if i don't have any more slots to create a game giveaway

You can ask support for more slots, but the way to run out is by deleting giveaways or have not received so be careful with those!

As Maruten said, open a support ticket about it.
If you delete your account, there's a one year cooldown for re-registering.

You'll get more slots for every 3 successfully delivered giveaway, so if you have working keys, you won't run out of slots.

You start with 3 slots and gain 1 additional slot for every 3 games that are marked "received" by the winners. You lose 1 slot for every giveaway you delete or if it is marked "not received" by the winner.

If you made some mistakes and lost your slots, you can create a support ticket here and request for more. It may take some time though because support can be slow.

I see that you created a giveaway that ended 2 weeks ago and has not been marked as received yet. Did you send the game to the winner and they have not responded? If they activated the game on their Steam account, but didn't mark it as received, I would try to contact them and ask them to mark it as received. Or you can create a support ticket under the category "request received feedback". They have 7 days to activate the game. If you tried sending them the game and they are not active on the site or ignoring you, you can request a new winner. There should be a button next to the winners name on this page to request for a new winner.

Once the winner of that giveaway marks it as received, it will be completed and you will get that giveaway slot back so you can create another. Every 3 times you do this you will get another slot. If you keep creating giveaways, soon you will have plenty of slots.

There's a lot more info in the FAQ and Guidelines.

Maybe try successfully delivering your first two GAs before asking for more ...