Well, congratulations mate.
It's really hard to become a Jr. Member nowadays,
it's really hard to obtain Merits :-(
Anyway yes, you can start to join some signature campaigns

Sad to say but it's only for the likes of you buddy. How come did I reached Full Member with 140 Merits if its hard to get one?
I advise you to read my tips 👇
https://bitcointalk.org/index.php?topic=5097635.0
Actually, Juniors isnt suppose to be participating on bounties or signature campaigns not until they reach the Member Rank. Its for your own good.
Classic pajeets does that kind of thing but as for the OP, I think he has some good points to be considered. And just a little bit more he will reach the next rank.