A couple of considerations.
1. The first is that everyone struggles with fingering at first. It's a completely normal part of the learning guitar process. Time and hands on practice on nuancing technique is the balm. If you find it's not working for you after a reasonable time, and can't analyse and detect by yourself why, watch the lesson again into ensure you are applying all aspects relative to fingering and haven't overlooked something. Otherwise, it's just practise, and more practise; on proviso,
2. Your guitar is actually a comfortable physical fit for you. This is more critical the smaller your hands and fingers usually proportionate with arm length, or if smaller framed IMV&PE. You offer no indication of your height or build. If you were petite, a Grand Concert might still be a poor fit. Let comfort be your guide.
Average height, I have medium-smaller hands/fingers, and find Cmaj and Dmaj are two of the easier open chords for me to to play on any guitar or string spacing. C does involve a modest stretch, but not a challenging stretch unless one had a truly minuscule span. Fmaj OTOH is a stretch just as Amaj is crowded if played with three fingers regardless how fingered.
If you're comfortable with your GC guitar, the issue will in resolved all likelihood by more time hands on assimilating those new found motor skills along with nuancing their minutae in the process.
PS. I intended to include this link in case you aren't already aware of it.
