Yeah but... that is 900 times more work...
more work for who? nobody as far as I can tell. 900 people make 900 donations. The project coordinator takes one lump of money. That's one piece of work for each person involved. If you expect a few big whales to jump on board and huzzah the project is done then 2btc is an absurdly low limit. If you want it to be a place for angels to dump on people, you need to make the site more explicitly oriented to that. If you want it to be a place for a community to fund a project, you need to allow the community to do what they think is most appropriate to get that done, which isn't always at least Xbtc.
I'm conflicted about the purpose of your site. It looks like a way to scrape money together for a project, but it requires a minimum donation.
It's a good idea but forcing arbitrary restrictions on your users without a strong business case seems like you're only limiting your market and not achieving a particular business goal.
"greater contributions" will equal to a higher success rate
Fair enough if that's your decision, but if a 2btc limit is the lowest donation, you could still end up with many 2btc donations to get any decent project running. It's such a 'picked from the air' limit... it weakens the purpose of your idea. It needs to be 'big donations only' or 'any size' so that people get a good sense of what you're trying to achieve. This current limit just causes confusion.
As the administrator it is my responsibility to make sure projects can get funded within the time limit
This seems like a strange requirement to place on yourself. How can you be responsible if people simply don't want to contribute? I would have thought your service is a 'build it and they will come' situation more than a 'build it and I will make sure they come' arrangement.
As a final word of encouragement, because I do genuinely like your idea, have a look at how kickstarter does this. Have a look if they have limits. Look at their most popular projects and (if you can) find out what kind of amounts were donated. Let's not pretend - this is a blatant kickstarter copy. Learn from them and improve upon what they've already figured out.