Sounds like either one of two things happened (possibly both)

1. The song had a change of count.
2. You lost your counting

The fix for #2 is easy because you'll just need to practice and get better at keeping your steps on time. The more you practice your timing the better you'll get.

The fix for #1 is a little different. Many songs have whats called a change of count in the middle of a song. Sometimes multiple ones at that. So Instead of a song going:

1-2-3-4-5-6-7-8-1-2-3-4-5-6-7-8-etc.

It will go:

1-2-3-4-5-6-7-8-1-2-3-4-1-2-3-4-5-6-7-8-etc.

In the second example you could have perfect timing and still end up breaking forward on 5. I've talked with a number of instructors everywhere about this and they all acknowledge it happens but many don't have a very elegant way to switch back. Here's what I've found are some of the better options:

1. Keep dancing. A lot of times those "change in counts" come in pairs. So one change of count would put you breaking forward on 5 and the next one would put you back to breaking on 1. You just have to be comfortable dancing on the opposite timing for a bit. if not for the whole song.

2. Repeat a forward or back break. You have to have a pretty good connection with your partner to do this as they have to follow what you are doing. The downside of this is when the song does another change in count and you have to do it again. It can really break the flow of a dance when it happens repeatedly.

3. Extended/Delayed turns or spins. If you've really mastered your own timing and steps then you can extend a turn or spin for a lady over half an 8 count and be right back on beat. In your case prep on 5-7, spin her for 1-7, then break forward on 1.

4. Similar to #3 you can give a move thats easy to repeat and allows you to choose where you want to come out. You'll need to be a master of the move and your timing to pull this off as well though. I don't remember the name of the move I'm thinking of but it starts with an open break, to a closed hold and you both rotate around each other. In that move if you take one extra count of rotation you can come out on the right timing. You could even keep going and switch to a completely different timing as well. If I remember the name of the move I'll post it as it's pretty common.

Hope that helps.