The SRS system here tries to maximise the efficiency of getting words into your long term memory by testing on you just before you are going to forget them. But forgetting is not a problem. When you get an answer wrong you get tested on it more frequently again and it will get into your long term memory with time, you just need to stick with the system.
Have you read the FAQ and the guide that are linked to in the Welcome Post? As well as using SRS, this site tries to help you remember things by building stories and memories around the mnemonics. If you get into the habit of doing that well it will help with your retention. I like to try and imagine each story taking place in a real location I know and find that helps with my retention of the story.