It is not grammatically correct Old Norse. What you're probably trying for
is:
"Pertti(r) á ást(ina) Kirsi(ar)."
But that's certainly not idiomatic Old Norse. I've never heard the phrase
"own love" in that language. The usual way to say it would be with the
verb 'unna'.
"Pertti ann Kirsi." (Pertti loves Kirsi.)
This would be perfectly good ON. In the younger fuþark you could write it
somewhat like this:
birti:An:kirsi
Where 'A' is the 'áss' rune and ':' is some word-separating glyph.
If you want something a bit more elaborate you could add something from
the historical inscriptions I mentioned.
"Pertti ann Kirsi af ástum ok af öllum huga."
Very difficult to translate properly but means something like:
"Pertti loves Kirsi with passionate love and all his mind."
If you're interested in that one you can try to find a picture of the
original inscription. Failing that we could render it one way or another
for you.
If it's too long you could shorten it to:
"Pertti ann Kirsi af öllum huga."
birti:An:kirsi:af:alum:huka (27 glyphs)
or skip the separation glyphs (who needs them?):
birtiAnkirsiafalumhuka (22 glyphs)
(Meaning: Pertti loves Kirsi with all his "mind".)
'Hugi' isn't quite "mind", it's hard to translate with a single English
word. It has connotations of 'soul' and 'bravery'.