Name for a condition where one with their limited knowledge thinks of a problem as bigger than it really is?
I can't provide you with a direct term that you are looking for. However, I think the level of confidence comes close.

My reasoning is as follows: Experience/knowledge increases task proficiency (Kuhlthau, 1999). Proficiency affects the level of confidence. Confidence, in turn, affects the perceived task complexity (Chang, 2005).

References
- Kuhlthau, JASIST (1999); 50(5): 399-412
- Chang, Computers Human Behav (2005); 21(5): 713-28