why can't you say אני בהווה?
Should be accepted, נמצא is not necessary here.
It is accepted now.
ani neemtzá ba-hoveh
אני בתוך המתנה is also ok? It makes no sense...
It's OK if you mean 'present' as in 'gift'.
Does אני בתוך בהווה make sense?
Not quite. The present doesn't really have an inside and an outside, so it sounds a bit strange to say "I am inside the present".
I put the right answer and it gave me it to me as wrong
In case it's helpful, this use of מצא in the Niphal meaning "be" goes back to Mikra (e.g., Deut 17:2; Isa 35:9, etc).