Perry, I scan it as you did in the first line: a tet line with two anapests and two iambs.
Whether you feel that that's a comfortable substitution in a generally IP poem depends on (a) the context of the poem that we're not given, so I can't comment on it, and (b) your ear.
For my part, I think the two-anapests-for-three-iambs substitution can work quite well, if used judiciously. The key of meter is finding some kind of equality: there's equality of stresses and equality of syllables. The ear can hear both, so you can use both—you've just got to sound it out and see if it works.
Without knowing the rest of your poem, I of course can't say whether it's judicious in this context or not.
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