Online courses require time. Usually you’ll have at least one assignment and one activity to do per week. Sometimes you will have discussion responses due by mid week. What that means is that you need to schedule time for your online class just like you would if you had to be in an on campus class.
Try to log in to your course at least 3 times a week. Set a day and time that works for you--maybe once mid week, once at the end of the week, and once on the weekend. Set reminders on your smartphone so that you stick to your schedule.
If your assignments are due on Sunday, make sure you’re working on the assignment during the week so that if you don’t understand, you have time to ask a question during the week when your instructor might be more readily available. It would be awful to start a paper on a Saturday that’s due Sunday only to need clarification and expect it in a few hours. More than likely it’s not going to happen.
Your grade in your online class will be a direct reflection of the time and attention you give it.