Reached Wave 6 in Level 3 in Soulkeep

In my daily playing of soulkeep and as I am on level 3, I have rented some cards and spells to help me passing this level and it is almost done but in the last few seconds 3 fiends passed the gate and I have lost but at all I know the mistake and I know what should I have do in the next try .

I have played this level using strong towers one of them surely is Amped Zapper which I consider one of the strongest towers in the game and the other one is regular gloom owl which is also so good and charnel pit and I call it the joker in each battle as it could hit almost all type of fiends.

For Spells in this level I have used Stew of Doom and also Mana Mania which is also good one as it gives booster to earning mana in each level but it can be used three times and I have used it in the first waves and this was another mistake that I have taken in this level too.

In the first 5 waves things was going so good and towers like twisted tempest and its place near the gate was doing amazing work with fiends that escape from first line of defense but in the wave 6 although I have more than 300 Mana I have chosen to upgrade towers rather than adding new one and it is so good until last 5 fiends which was a surprise that they came out near the gate and passed it.

The mistake that I have taken and it was enough for me to pass the level that I used all stew of doom in the first waves and in the last wave which was the hardest one, There is no stew of doom to be used so I was defeated and all I needed is 5 fiends to be killed using stew of doom or other tower to be near my gate.