your tx fee is very very low... this could take some time. even without an attack
I know and i regret now. Is it possible to undo things? to send somehow a bigger fee for that transaction? sorry if it is a stupid question but I am desperate.
Yes. Two ways:
1. You can either create a new transaction using the same inputs and a higher fee, hoping for this double spend to confirm.
2. Spend the change output with a high fee, and hope for a pool practicing child-pays-for-parent to pick up both and confirm them. Eligius, EclipseMC and possibly others do this.
Method 2 has a higher probability of success, as the double spend will have problems getting relayed to the miners.