You're right, could be just a weed, but compared to all the other ficus species i've sprouted this year, it looks like a ficus. Here's some more pictures of my windowsill bonsai project.
Started last year, had luck with germinating 5 different species: Religiosa, Carica, Salicifolia, Cordata, and Microcarpa.
This year ive successfully germinated 13 different species: Elastica (in question here?), Religiosa (again), Racemosa, Benjamina, Aurea, Ingens, Pumila, Rubiginosa, Natalensis, Austrocaledonica, Brandgeei, Semicordata, and finally Abutilifolia.
Giving me a total of 17 different ficus species.
From October they will go under grow light to "overwinter", like last year. The thing with ficus, is they grow like crazy all year even in winter time.
Those on top are pre bonsai experiments, they've been trunk chopped completely (growing new trunks). However i regret doing that, they took all summer to recover. So the only two (close to)-bonsai ive got are the little mame willow leaf and the two namaqua figs that ive spun together. It take a loong time to go from seed to bonsai. Lol. All these are 1 year and 3 months old.
And i use distilled water only, ive made my own distilling coils. Take 24h to make 10 litres which last me a month. I do this to remove all calcium from the water, eliminating phytotoxicity and to avoid calcium deposits on the leaves when misting them. Just like rain water

In fact, it IS rain water. Only artificially made in my kitchen. What a global pandemic doesn't do to you...