update config.json

openlane/user_project_wrapper/config.json

diff --git a/openlane/user_project_wrapper/config.json b/openlane/user_project_wrapper/config.json
index b11ce49..6f1133c 100644
--- a/openlane/user_project_wrapper/config.json
+++ b/openlane/user_project_wrapper/config.json
@@ -29,8 +29,8 @@
     "DIE_AREA": "0 0 2920 3520",
     "RUN_CVC": 0,
     "UNIT": 2.4,
-    "FP_IO_VEXTEND": "expr::2*ref::$UNIT",
-    "FP_IO_HEXTEND": "expr::2*ref::$UNIT",
+    "FP_IO_VEXTEND": "expr::(2*ref::$UNIT)",
+    "FP_IO_HEXTEND": "expr::(2*ref::$UNIT)",
     "FP_IO_VLENGTH": "ref::$UNIT",
     "FP_IO_HLENGTH": "ref::$UNIT",
     "FP_IO_VTHICKNESS_MULT": 4,
@@ -44,8 +44,8 @@
     "FP_PDN_CORE_RING_HSPACING": 12.45,
     "FP_PDN_VWIDTH": 3.1,
     "FP_PDN_HWIDTH": 3.1,
-    "FP_PDN_VSPACING": "expr::5*ref::$FP_PDN_CORE_RING_VWIDTH",
-    "FP_PDN_HSPACING": "expr::5*ref::$FP_PDN_CORE_RING_HWIDTH",
+    "FP_PDN_VSPACING": "expr::(5*ref::$FP_PDN_CORE_RING_VWIDTH)",
+    "FP_PDN_HSPACING": "expr::(5*ref::$FP_PDN_CORE_RING_HWIDTH)",
     "VDD_NETS": ["vccd1", "vccd2","vdda1","vdda2"],
     "GND_NETS": ["vssd1", "vssd2","vssa1","vssa2"],
     "SYNTH_USE_PG_PINS_DEFINES": "USE_POWER_PINS",