The university that gave me an offer only gave me two weeks to accept the offer. I asked them for an extension, and they only gave me a week more. I have still yet to hear from the other universities I applied to; since it is only mid March. I am quite confused as to what I should do, I don't want to give back the offer after accepting it. But I also can't predict what the other universities decisions would be and neither am I too confident as to reject the one offer I do have. Would appreciate some advice. I applied to Masters program in Physics, in Canada.
Presumably the school you heard from was not your first choice.
I'd just be as upfront as possible, with everyone. Next step is probably to contact the schools and/or professors you haven't heard from, say that you have another offer, and ask if they can give an update on the timing of their decisions.
Depending on what those schools say, contact the school you were accepted to and request another extension until the specific dates that the other schools gave you.
Clearly accepting the offer without mentioning the possibility of declining it later is a lie. And YOU have to make the decision whether it is acceptable to lie in this case or not.
As I was in the same situation, I also wondered what to do. Here is the decision that I have made for myself:
When applying for a Bachelor or Master degree program, accepting an offer has little consequence for the offering institution. There is no scholarship attached that could be offered to another candidate and there are quite a few places to begin with, so departments may presume that some accepted offers will be rejected later. Personally, for me I could live with lying to the institution in this case.
When applying for a PhD program the institution will make plans for you after accepting an offer. That is, assign teaching duties and allocate funding for you. If the accepted offer is rejected at a later point, this will cause a great deal of trouble for the institution. Personally, for me it would not be okay to lie to the institution in this case.
So, that is what I did. (I applied for PhD positions) I accepted my less favored offer and withdrew my applications at other institutions. If one of the other institution had given a life changing offer to me, I might have reconsidered, but the benefit for me would have had to be gigantic to offset the damage I would have been doing to the less favored institution. After all, even if you do not care about the well-being of your less favored institthat would be burning a bridge, and some fields of research are so small that it can harm your career very badly having burned that bridge.