。
I managed to get there on time somehow.
Literal
I [topic-は] somehow time [by-までに] there [to-に] arrived.
なんとか ('somehow, just barely') signals effort against difficulty — the speaker made it, but only just. までに marks a deadline ('by'), distinct from まで ('until'): までに means you must complete the action by that point, まで means you continue up to it.