Impossible To Progress On Colosseum

There's nothing that can be done wrong, it's poorly designed. Can't level up Mara without progressing, and you can't progress without leveling her up. Can't even level up the other charcters she's fighting with. It's a mess. I'm already level 13 on the Episode track and it offers 0 currency on being able to level anyone up. 

I'm f2p also and at the same place as you. But the OP might have a point, especially if they didn't start playing Coliseum daily at the very beginning of the era.

Silver Marja on YouTube ran into a situation where he started a f2p account about 4 or 5 days into the era. He ended up getting locked because he couldn't progress to get resources and couldn't get resources to progress (https://youtu.be/d0e6np6xgNM?si=oyovAKTHDpM769a5&t=74). It's a different situation from the OP, but I wouldn't put it past CG's design and tuning of Coliseum. 

I wonder if OP isn't getting the loaned unit upgrades for some reason? There are a few posts in the forums about that.