welcome to the waiting game! the process is stressful. But - it's wayyyyyy to early for you to worry!! if you start like this, you won't make it through the whole immigration process! so calm down, and take the days one at a time, and also, try to see the positive parts!
First - you applied in December, and from the december spreadsheet, you can see that quite a few have been approved for first stage in 20 to 30 days, where the website indicates 50 days - so most likely you'll hear soon about your first stage.
first stage is about the sponsor: Do you live in Canada, or did you provide proofs that you will be returning as soon as PR is approved? if you have no criminal background and not on welfare, then you will be approved. So - no need to stress about that part. just wait, look at the spreadsheet and you'll know when your turn will come.
Lots of people met online and were approved, so no worries about that. Second marriage is not necessarily a problem, if your current one is genuine and you have added proofs in your application, you'll be OK. Also - if they have doubts, they will ask for more proofs, or for an interview, but won't deny your PR up-front. So - until you are asked for more proofs, assume that your application will be fine. IF/when asked for more proofs, then you have time to worry about it! in the meantime, if you are not living with your husband, collect proofs of on-going relationship (trips to see each other, phone, skype records etc). if you're living with your husband, keep pictures of outings together, trips etc. it's the best way to prepare - most likely you won't be asked for it, but in case, then you're ready...
Also - your husband is from the US, so he is not suspected to marry to gain access to Canada, or to a better life standards etc - so they will evaluate if your relationship is genuine, but they also know that with an US passport, it's likely that the only reason why he is trying to come to Canada is because you are there, nothing else.
So - relax, breathe, and don't think too much about possible problems - if you start comparing with other applications you'll always feel like you have not sent enough proofs, you could have done better etc. Instead, trust yourself, and trust that you have put together the best application possible and you will be approved quickly.
Cheers,
Sweden