Hello,
Don't take anything I say here as gospel because I'm not studying 90 credits myself. As far as I'm aware, you should be able to study the remaining level 1 course and 60 credits of the level 2 courses next year if you study 90 this year. The only exception to this should be if the level 2 courses have the level 1 course you missed as a requirement.
I'll use the example of the degree I'm studying, Computing & IT and Mathematics. If I took TU100 - My Digital Life (60 credits) and MST124 - Essential Mathematics 1 (30 credits) in one year. The following year I could study MST125 - Essential Mathematics 2 (30 credits) to round out level 1 and also take 60 credits of level 2 Computing modules, because these mostly only rely on TU100. Some also require MST124. I could not, however, take one of the 60 credit second year Mathematics courses as these require MST125 to have already been completed.
This is fairly simple for studying 2 subjects as they generally don't require modules from each other at the next stage. For studying a single subject, if you are, it might be more awkward. Make sure to check the module pages for required modules from previous stages. It's possible that some level 2 courses aren't reliant on all of your level 1 courses, so it's worth a look. If you tell me what subject(s) you're studying I'll happily look into this for you.
I hope this helps. Good luck.